[#1247] *: Clarify docs about returned errors from apistatus package

`apistatus` package provides types which implement build-in `error`
interface. Add `error of type` pattern when documenting these errors in
order to clarify how these errors should be handled (e.g. `errors.Is` is
not good).

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/local_object_storage/blobstor/delete_big.go

@@ -21,7 +21,7 @@ type DeleteBigRes struct{}
 // Returns any error encountered that did not allow
 // to completely remove the object.
 //
-// Returns apistatus.ObjectNotFound if there is no object to delete.
+// Returns an error of type apistatus.ObjectNotFound if there is no object to delete.
 func (b *BlobStor) DeleteBig(prm *DeleteBigPrm) (*DeleteBigRes, error) {
 	err := b.fsTree.Delete(prm.addr)
 	if errors.Is(err, fstree.ErrFileNotFound) {

pkg/local_object_storage/blobstor/delete_small.go

@@ -17,7 +17,7 @@ type DeleteSmallRes struct{}
 // Returns any error encountered that did not allow
 // to completely remove the object.
 //
-// Returns apistatus.ObjectNotFound if there is no object to delete.
+// Returns an error of type apistatus.ObjectNotFound if there is no object to delete.
 func (b *BlobStor) DeleteSmall(prm *DeleteSmallPrm) (*DeleteSmallRes, error) {
 	return b.blobovniczas.delete(prm)
 }

pkg/local_object_storage/blobstor/get_big.go

@@ -24,7 +24,7 @@ type GetBigRes struct {
 // Returns any error encountered that
 // did not allow to completely read the object.
 //
-// Returns apistatus.ObjectNotFound if requested object is not
+// Returns an error of type apistatus.ObjectNotFound if requested object is not
 // presented in shallow dir.
 func (b *BlobStor) GetBig(prm *GetBigPrm) (*GetBigRes, error) {
 	// get compressed object data

pkg/local_object_storage/blobstor/get_range_big.go

@@ -27,7 +27,7 @@ type GetRangeBigRes struct {
 // did not allow to completely read the object payload range.
 //
 // Returns ErrRangeOutOfBounds if requested object range is out of bounds.
-// Returns apistatus.ObjectNotFound if object is missing.
+// Returns an error of type apistatus.ObjectNotFound if object is missing.
 func (b *BlobStor) GetRangeBig(prm *GetRangeBigPrm) (*GetRangeBigRes, error) {
 	// get compressed object data
 	data, err := b.fsTree.Get(prm.addr)

pkg/local_object_storage/blobstor/get_range_small.go

@@ -21,7 +21,7 @@ type GetRangeSmallRes struct {
 // did not allow to completely read the object payload range.
 //
 // Returns ErrRangeOutOfBounds if requested object range is out of bounds.
-// Returns apistatus.ObjectNotFound if requested object is missing in blobovnicza(s).
+// Returns an error of type apistatus.ObjectNotFound if requested object is missing in blobovnicza(s).
 func (b *BlobStor) GetRangeSmall(prm *GetRangeSmallPrm) (*GetRangeSmallRes, error) {
 	return b.blobovniczas.getRange(prm)
 }

pkg/local_object_storage/blobstor/get_small.go

@@ -19,7 +19,7 @@ type GetSmallRes struct {
 // Returns any error encountered that
 // did not allow to completely read the object.
 //
-// Returns apistatus.ObjectNotFound if requested object is missing in blobovnicza(s).
+// Returns an error of type apistatus.ObjectNotFound if requested object is missing in blobovnicza(s).
 func (b *BlobStor) GetSmall(prm *GetSmallPrm) (*GetSmallRes, error) {
 	return b.blobovniczas.get(prm)
 }