Replaces instances of "recent topics" in the web-app and documentation
to be "recent conversations".
Renames both `recent-topics.md` files in the help center to be
`recent-conversations.md` and updates/redirects links to new URL.
Does not update instances of "recent topics" in frontend code comments
and does not update the main overview changelog, for now.
Does not change case study text where "recent topics" was referenced
in a quote, but does change generic text references to be "recent
conversations".
This better matches the title of the page and more generally our
conventions around naming /help/ articles. We include a redirect
because this is referenced from Welcome Bot messages, and we
definitely don't want those links to break.
This renames references to user avatars, bot avatars, or organization
icons to profile pictures. The string in the UI are updated,
in addition to the help files, comments, and documentation. Actual
variable/function names, changelog entries, routes, and s3 buckets are
left as-is in order to avoid introducing bugs.
Fixes#11824.