Epic: Add official tag to feeds

[emmambd]

Describe the problem

Consuming applications need to know if a GTFS feed is "official", meaning that it's approved by the transit authority it represents and should be used for riders.

For #784, users need to be able to

• Mark a feed as official in the Add a Feed form
• See that a feed is official in the API

Proposed solution

Solving this problem has 2 main parts:

1. Adding the official tag to the catalogs, API and UI so it's possible for us to flag this. Should include timestamp of when it was marked official.
2. Automating the process of identifying when a specific feed is official. This likely includes contacting the agency directly and asking them, and then updating the official status when they say "yes".

Alternatives you've considered

No response

Additional context

No response