Cohort revision lock should be clearer to end users

[James Simpson]

Recently I ran across an issue where I could see that a newer version of a snap was available, but refreshing wasn't pulling it in:

jsimpso@ghastly:~$ sudo snap refresh --channel=3.2/stable maas
maas (3.2/stable) 3.2.1-12003-g.a2a841dfb from Canonical✓ refreshed
jsimpso@ghastly:~$ sudo snap info maas | grep installed
installed: 3.2.1-12003-g.a2a841dfb (23093) 147MB in-cohort
jsimpso@ghastly:~$ sudo snap info maas | grep 3.2/stable
tracking: 3.2/stable
  3.2/stable: 3.2.2-12005-g.f0f96fa78 2022-08-08 (23178)
147MB -
  jsimpso@ghastly:~$ sudo snap refresh maas --channel=3.2/stable
  snap "maas" has no updates available

This ended up being caused by this server being part of a cohort. Which is great, because that's exactly what cohorts are supposed to do! However, I think the messaging around this could be somewhat improved. It does tell me in the output above that there's a cohort in play, but I completely missed the "in-cohort" stamp on the "installed" line because I was focusing on the version number.

Rather than "snap has no updates available", it would be great it we could acknowledge that there *are* updates available, but our cohort has us locked into the current revision for {x} additional days.

Thanks!