Feature Request: Mainline v4.0.x - Follow hashtags

[politas]

Mastodon 4.0.x introduced new API endpoints to allows users to follow hashtags

https://github.com/mastodon/mastodon/pull/18809 https://github.com/mastodon/mastodon/pull/19472

Not implementing these endpoints and the overall feature will leave a bad user experience for app users. Web UI implementation - https://github.com/mastodon/mastodon/pull/18862

I believe Hashtag following is a good feature to support to make it easier for people to see the conversations they are interested in without having to track down and follow people who may also post prolifically on other topics of less interest.