[#872] object: Introduce APE middlewar for object service

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

pkg/services/object/request_context.go

@@ -0,0 +1,16 @@
+package object
+
+import "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/acl"
+
+type RequestContextKeyT struct{}
+
+var RequestContextKey = RequestContextKeyT{}
+
+// RequestContext is a context passed between middleware handlers.
+type RequestContext struct {
+	Namespace string
+
+	SenderKey []byte
+
+	Role acl.Role
+}