Uses new `select-stream-view-general.md` for instructions.
Also, clarifies location of button/icon as well as the
header for the privacy setting in the update modal.
Finally, updates save instruction to use `save-changes.md`.
This commit includes a new `stream_post_policy` setting,
by replacing the `is_announcement_only` field from the Stream model,
which is done by mirroring the structure of the existing
`create_stream_policy`.
It includes the necessary schema and database migrations to migrate
the is_announcement_only boolean field to stream_post_policy,
a smallPositiveInteger field similar to many other settings.
This change is done to allow organization administrators to restrict
new members from creating and posting to a stream. However, this does
not affect admins who are new members.
With many tweaks by tabbott to documentation under /help, etc.
Fixes#13616.
Lauryn Menard
Anders Kaseorg
Ryan Rehman