Gateway should validate schema delegations when posting content

[JoeCap08055]

Description

Message content, since it is batched, is currently unable to have individual message schema delegations verified on-chain when posting. Therefore, the Provider application (as provided by content-publishing-service and content-watcher) should perform this validation both before adding content to a batch, and upon retrieving content from the chain.

• [content-publishing-service] Add schema delgation validation for content publishing requests #704
• [content-watcher] Add schema delegation validation to retrieved content #705