Release 6.0.0
Make TM recover from TO being unavailable at startup (#6146)

* Make TM recover from TO being unavailable at startup

Always set non-nil TO sessions that can eventually authenticate
themselves when TO recovers. Additionally, instead of exclusively using
one major client version after starting up and logging in, always
attempt the latest major version and fall back to the legacy version in
case of error. This will allow TM to seamlessly transition between using
either major version no matter which order TM and TO are upgraded in.

Closes: #6129

* Organize imports, add UsingDummyTO back

(cherry picked from commit 16dda648671ad438fcb8b6b08eaf6fbeb2fa9589)
5 files changed