Refactor pmbootstrap status git repos output (pmaports "workdir is not clean" should not be an error)

I've seen in the postmarketOS-porting channel, that this causes confusion:

$ pmbootstrap status                   
[21:04:04] *** CONFIG ***
[21:04:04] Device: qemu-amd64 (x86_64, "QEMU amd64")
[21:04:04] Kernel: virt
[21:04:04] User Interface: weston
[21:04:04] 
[21:04:04] *** GIT REPOS ***
[21:04:04] Path: /home/user/.local/var/pmbootstrap/cache_git
[21:04:04] - aports_upstream (master)
[21:04:04] - pmaports (master)
[21:04:04] 
[21:04:04] *** CHECKS ***
[21:04:04] [NOK] pmaports: workdir is not clean
[21:04:04] 
[21:04:04] *** CHECKLIST ***
[21:04:04] - pmaports: consider cleaning your workdir
[21:04:04] - Run 'pmbootstrap status' to verify that all is resolved

[NOK] pmaports: workdir is not clean indicates that something is wrong, although it's normal that the workdir is not clean when doing a port. So pmbootstrap should not show an error there, maybe have it as reminder next to the git repo instead or something.

On a related note: now that the pmdevices git repository is not coming, I'm re-thinking the whole *** GIT REPOS *** section of the output. The only git repo that really matters for users is "pmaports". "aports_upstream" is only used for things like "pmbootstrap aportgen --fork-alpine", and there we don't expect anyone to touch the repository. So there is not much use in displaying the aports_upstream repo status. It might be better to have a *** PMAPORTS *** block there instead, where we can display the properties a bit nicer than in just one line.

I think it would be nice to add the current release channel, on which the currently checked out branch is (as read from pmaports.cfg).

I'll probably look into this after my patchset for #1855 (closed) is merged (as this adds the channels related code).

Recommendations, how you would like to have it, welcome.