MM-49564: Drafts upsert in the Store vs App layer (#22530)

* MM-49564: Upsert in the Store vs App layer

Refactor drafts so that Upserting a draft would happen in the DB and not
in the app layer.

* Fixes mocks

* Fixes tests

* Fixes translations

* Fixes tests

* Update tests

* Fixes tests

* Addresses review comments

- renames Save => Upsert
- removes Sleep from tests

* Fixes flaky test

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/store/store.go

@@ -985,11 +985,10 @@ type PostPriorityStore interface {
 }
 
 type DraftStore interface {
-	Save(d *model.Draft) (*model.Draft, error)
+	Upsert(d *model.Draft) (*model.Draft, error)
 	Get(userID, channelID, rootID string, includeDeleted bool) (*model.Draft, error)
 	Delete(userID, channelID, rootID string) error
 	GetDraftsForUser(userID, teamID string) ([]*model.Draft, error)
-	Update(d *model.Draft) (*model.Draft, error)
 }
 
 type PostAcknowledgementStore interface {