[bug] Add missing group property to the Account model (#3746)

* Stub out account's Group parameter

* Fix typo in Contributing documentation

* Update swagger and match style

* Update the swagger command to mimic test/swagger.sh

* Fix tests for new `group` param in Account model

* More test changes for new `group` param in Account

* Continuing test changes for `group` param stubbing

* Another round of `group` stubbing for tests

docs/api/swagger.yaml

@@ -300,6 +300,10 @@ definitions:
                 format: int64
                 type: integer
                 x-go-name: FollowingCount
+            group:
+                description: Account identifies as a Group actor.
+                type: boolean
+                x-go-name: Group
             header:
                 description: Web location of the account's header image.
                 example: https://example.org/media/some_user/header/original/header.jpeg
@@ -2439,6 +2443,10 @@ definitions:
                 format: int64
                 type: integer
                 x-go-name: FollowingCount
+            group:
+                description: Account identifies as a Group actor.
+                type: boolean
+                x-go-name: Group
             header:
                 description: Web location of the account's header image.
                 example: https://example.org/media/some_user/header/original/header.jpeg