Add GridStoreAdapter and FSAdapter Config

[cbaker6]

Added documentation for the following PRs:

• https://github.com/parse-community/parse-server-fs-adapter/pull/15
• https://github.com/parse-community/parse-server/pull/6765
• https://github.com/parse-community/parse-server/pull/6768

[davimacedo]

Sorry guys. I should have waited https://github.com/parse-community/parse-server/pull/6768 to be released. But I plan to do a new release of Parse Server this weekend and we should be fine then.