Added account featured tags API

[noellabo]

Only works with local accounts until #11595 is merged.

• GET /api/v1/accounts/:id/featured_tags
• returns id of Tag, not FeaturedTag
• Since it can be obtained from the public profile without authentication, the API is also not authenticated

[{"id":"606","name":"#distsns","url":"https://fedibird.com/@noellabo/tagged/distsns"},{"id":"1069","name":"#リレーの話","url":"https://fedibird.com/@noellabo/tagged/%E3%83%AA%E3%83%AC%E3%83%BC%E3%81%AE%E8%A9%B1"},{"id":"611","name":"#test","url":"https://fedibird.com/@noellabo/tagged/test"},{"id":"1043","name":"#fedibird","url":"https://fedibird.com/@noellabo/tagged/fedibird"}]

[noellabo]

Would it be better to use just name without using tag id?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[Gargron]

Not stale

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.