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

[politas]

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

mastodon/mastodon#18809
mastodon/mastodon#19472

Not implementing these endpoints and the overall feature will leave a bad user experience for app users.
Web UI implementation - mastodon/mastodon#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.

[weex]

Interesting. It seems this feature allows a user to follow uses of a hashtag from a remote server. Not being able to do that or support remote follows does sound like a valid problem to me.

[politas]

It's a great feature for small community and single user servers, where just searching on, say, #fediblock shows you nothing, because users on your server aren't following the people posting to it.

[politas]

Additional related PRs, I believe

mastodon/mastodon#21285 - Fix not being able to follow multiple hashtags
mastodon/mastodon#21437 - UI fix from "user" to "message" (not yet merged)

[weex]

Looked into the first upstream PR and it depends on at least three others with changes around trending and customizable user roles. Unfortunately this makes migrating any of the related code from Mastodon infeasable but on this upside, this is a great opportunity to implement a minimal solution that doesn't touch so many other areas.

I think we should split the issue in two. One for following hashtags from other servers (i.e. a client role) and another for providing endpoints that enable users on other servers to follow hashtags on Ecko servers.