Add "Unlisted" option for toots.

[Xabellee]

Web Mastodon supports that feature, but in this app I cannot use it. In this app I can only use public, Followers only, Only people I mention.

[moertel]

Some other threads (e.g. on the iOS app) talk about this being a deliberate design decision. Before anyone goes in to invest time in a PR, can the maintainers please clarify whether this is true?

Edit: nevermind, meanwhile I found the linked PR and read the discouraging discussion within.

[Cassolotl]

This is now essential in light of mastodon/mastodon#26344, which will make all public posts from "discoverable" accounts searchable.