Add deletion of individual sessions

Implement a method to depeer by deleting existing sessions. The
batched creation method does not create an obvious collection resource
on the server side that may be used for a depeering situation therefore
this commit only implements individual session deletion.

To tackle a situation where depeering is desired for a whole metro or
IX while respecting this RESTful interface, we will need to define a
separate aggregate resource that can be used to operate atomically on
the set of target sessions.

api/openapi.yaml

@@ -115,12 +115,6 @@ paths:
           required: true
           schema:
             type: integer
-        - name: request_id
-          in: query
-          description: request identifier
-          required: false
-          schema:
-            type: string
         - name: max_results
           in: query
           description: Hint to paginate the request with the maximum number of results the caller is able to process.
@@ -148,6 +142,46 @@ paths:
         '403':
           $ref: '#/components/responses/ErrorResponse'
 
+  /sessions/{session_id}:
+    get:
+      description: Retrieves a given session by it server-generated ID provided on creation.
+      parameters:
+        - name: session_id
+          in: path
+          description: Server-generated stable identifier for the session.
+          required: true
+          schema:
+            type: string
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Session'
+        '400':
+          $ref: '#/components/responses/ErrorResponse'
+        '403':
+          $ref: '#/components/responses/ErrorResponse'
+
+    delete:
+      description: Requests to turn the session down and delete it from the server.
+      parameters:
+        parameters:
+        - name: session_id
+          in: path
+          description: Server-generated stable identifier for the session.
+          required: true
+          schema:
+            type: string
+      responses:
+        '204':
+          description: Session is scheduled for deletion and no longer usable
+        '400':
+          $ref: '#/components/responses/ErrorResponse'
+        '403':
+          $ref: '#/components/responses/ErrorResponse'
+
 components:
   schemas:
     Location: