[#56] object: Introduce Patch method

* Introduce rpc `Patch` and corresponding types;
* Generate docs.

Signed-off-by: Airat Arifullin <aarifullin@yadro.com>

object/service.proto

@@ -283,6 +283,51 @@ service ObjectService {
   // - **TOKEN_EXPIRED** (4097, SECTION_SESSION): \
   //   provided session token has expired.
   rpc PutSingle(PutSingleRequest) returns (PutSingleResponse);
+
+  // Patch the object. Request uses gRPC stream. First message must set
+  // the address of the object that is going to get patched. If the object's attributes
+  // are patched, then these attrubutes must be set only within the first stream message.
+  //
+  // If the patch request is performed by NOT the object's owner but if the actor has the permission
+  // to perform the patch, then `OwnerID` of the object is changed. In this case the object's owner
+  // loses the object's ownership after the patch request is successfully done.
+  //
+  // As objects are content-addressable the patching causes new object ID generation for the patched object.
+  // This object id is set witihn `PatchResponse`. But the object id may remain unchanged in such cases: 
+  // 1. The chunk of the applying patch contains the same value as the object's payload within the same range;
+  // 2. The patch that reverts the changes applied by preceding patch;
+  // 3. The application of the same patches for the object a few times.
+  //
+  // Extended headers can change `Patch` behaviour:
+  // * [ __SYSTEM__NETMAP_EPOCH \
+  //   (`__NEOFS__NETMAP_EPOCH` is deprecated) \
+  //   Will use the requsted version of Network Map for object placement
+  //   calculation.
+  //
+  // Please refer to detailed `XHeader` description.
+  //
+  // Statuses:
+  // - **OK** (0, SECTION_SUCCESS): \
+  //   object has been successfully patched and saved in the container;
+  // - Common failures (SECTION_FAILURE_COMMON);
+  // - **ACCESS_DENIED** (2048, SECTION_OBJECT): \
+  //   write access to the container is denied;
+  // - **OBJECT_NOT_FOUND** (2049, SECTION_OBJECT): \
+  //   object not found in container;
+  // - **OBJECT_ALREADY_REMOVED** (2052, SECTION_OBJECT): \
+  //   the requested object has been marked as deleted.
+  // - **OUT_OF_RANGE** (2053, SECTION_OBJECT): \
+  //   the requested range is out of bounds;
+  // - **CONTAINER_NOT_FOUND** (3072, SECTION_CONTAINER): \
+  //   object storage container not found;
+  // - **CONTAINER_ACCESS_DENIED** (3074, SECTION_CONTAINER): \
+  //   access to container is denied;
+  // - **TOKEN_NOT_FOUND** (4096, SECTION_SESSION): \
+  //   (for trusted object preparation) session private key does not exist or
+  //   has been deleted;
+  // - **TOKEN_EXPIRED** (4097, SECTION_SESSION): \
+  //   provided session token has expired.
+  rpc Patch(stream PatchRequest) returns (PatchResponse);
 }
 
 // GET object request
@@ -816,4 +861,70 @@ message PutSingleResponse {
   // authenticate the nodes of the message route and check the correctness of
   // transmission.
   neo.fs.v2.session.ResponseVerificationHeader verify_header = 3;
-}
+}
+
+// Object PATCH request
+message PatchRequest {
+  // PATCH request body
+  message Body {
+    // The address of the object that is requested to get patched.
+    neo.fs.v2.refs.Address address = 1;
+
+    // New attributes for the object. See `replace_attributes` flag usage to define how
+    // new attributes should be set.
+    repeated neo.fs.v2.object.Header.Attribute new_attributes = 2;
+
+    // If this flag is set, then the object's attributes will be entirely replaced by `new_attributes` list.
+    // The empty `new_attributes` list with `replace_attributes = true` just resets attributes list for the object.
+    //
+    // Default `false` value for this flag means the attributes will be just merged. If the incoming `new_attributes`
+    // list contains already existing key, then it just replaces it while merging the lists. 
+    bool replace_attributes = 3;
+
+    // The patch for the object's payload. 
+    message Patch {
+      // The range of the source object for which the payload is replaced by the patch's chunk.
+      // If the range's `length = 0`, then the patch's chunk is just appended to the original payload
+      // starting from the `offest` without any replace.
+      Range source_range = 1;
+
+      // The chunk that is being appended to or that replaces the original payload on the given range.
+      bytes chunk = 2;
+    }
+
+    // The patch that is applied for the object.
+    Patch patch = 4;
+  }
+
+  // Body for patch request message.
+  Body body = 1;
+
+  // Carries request meta information. Header data is used only to regulate
+  // message transport and does not affect request execution.
+  neo.fs.v2.session.RequestMetaHeader meta_header = 2;
+
+  // Carries request verification information. This header is used to
+  // authenticate the nodes of the message route and check the correctness of
+  // transmission.
+  neo.fs.v2.session.RequestVerificationHeader verify_header = 3;
+}
+
+// Object PATCH response
+message PatchResponse {
+  // PATCH response body
+  message Body {
+      // The object ID of the saved patched object.
+      neo.fs.v2.refs.ObjectID object_id = 1;
+  }
+
+  // Body for patch response message.
+  Body body = 1;
+
+  // Carries response meta information. Header data is used only to regulate
+  // message transport and does not affect request execution.
+  neo.fs.v2.session.ResponseMetaHeader meta_header = 2;
+
+  // Carries response verification information. This header is used to authenticate
+  // the nodes of the message route and check the correctness of transmission.
+  neo.fs.v2.session.ResponseVerificationHeader verify_header = 3;
+}