Merge ppa-dev-tools:add-ppa-credentials-command into ppa-dev-tools:main

A few minor comments and suggestions to improve before merging as we might never look back to it otherwise.

The "allow argument to specify output file" seems so easy that it should IMHO be added.
I mean any snap magic that needs to be research, yes that is later.
But allowing where to store, that should be so easy that we should not hold back on that.

And TBH a global arg (not per subcommand, but generally available) to pass a filename.
"--use-credential" (if no arg given also using the default path) and "--use-credential foo" which would do not more but load that into the environment variable - that also seems rather close. Like <1h of work.
So again, unless you already released by time pressure, please consider adding that right away.

Unfortunately this was kind of a "pull a loose thread from a sweater" problem, and ended up actually involving a more extensive amount of work than apparent. The credentials handling is pretty early on in the process (obviously) which made it tricky to tweak without breaking other things, but the good news is that the testsuite is extensive and thorough enough now that it was super helpful in spotting problems.

I've refactored the env var handling to be more general purpose, and layered in functionality to allow it to come from the specified file. I opted to name the option --credentials rather than --use-credentials to match the similar option --config.

I had initially hoped to split the review changes out separately to make it easier for you to check, but due to needing to add more fixes it was simpler to just merge all the rework into the main commits. Hopefully you can see what changed via range-diff, although since so much changed it may be worth just doing a fresh review from scratch.

+1 on refactoring the argparse and help text later in a separate PR - just make sure it is not forgotten

This MP LGMT now, the few things that came to my mind were too small to mention or known and can be done in follow up iterations.

Thanks, change landed to main:

$ git merge --ff-only add-ppa-credentials-command
Updating 06e6152..20533a7
Fast-forward
 ppa/constants.py | 2 ++
 ppa/lp.py | 53 +++++++++++++++++++++++++++++++++++----------------
 scripts/ppa | 87 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++----------
 tests/helpers.py | 13 ++++++++++++-
 tests/test_lp.py | 8 ++++----
 tests/test_scripts_ppa.py | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 185 insertions(+), 31 deletions(-)
$ git push origin
Enumerating objects: 33, done.
Counting objects: 100% (33/33), done.
Delta compression using up to 12 threads
Compressing objects: 100% (20/20), done.
Writing objects: 100% (23/23), 4.83 KiB | 1.21 MiB/s, done.
Total 23 (delta 17), reused 0 (delta 0), pack-reused 0
To git+ssh://git.launchpad.net/ppa-dev-tools
   06e6152..20533a7 main -> main