Rjwebb/let moderator manually change synced fields

[rjwebb]

This PR updates the "Configure" page for the conversations so that:

• syncing can be enabled/disabled for a given conversation
• if syncing is disabled, admins/owners can manually modify the fields that have been synced from GitHub

There are some miscellaneous fixes in here as well, such as:

• 882b15c use the @typescript-eslint/parser parser in eslint on the client, the babel-eslint parser flags some valid typescript syntax as being invalid
• use dotenv to inject environment variables into the client, this is the same method that we are using on the backend