Translate the pmaports channels "stable" to "v20.05" and "stable-next"
to "v21.03", so these have the same channel name as the pmaports.git
branch name.
The original plan was to switch the "stable" channel from the "v20.05"
branch to the "v21.03" branch when the release is done. However, now
that we are close to that, I'm realizing that this would not be useful.
It would lead to conflicts in the dir with locally built packages
(default: ~/.local/var/pmbootstrap/packages/$CHANNEL). And it would make
it awkward to go back to a previous branch (we may name it old-stable
for the time being, but what after that, old-old-stable?).
Prepare to base postmarketOS on Alpine stable by parsing the new
channels.cfg file in pmaports.git, that describes which channel
needs which branches and mirror dirs from postmarketOS and Alpine.
Use the information in pmb.helpers.git.get_branches_official() first,
more is coming in follow-up commits.
Read the file from origin/master, so we get the latest fetched version
even if the last checked out master branch is not up-to-date (think of
currently checked out release branch instead of master, master will
never be updated to point to latest origin/master). Allow to override
the file with a new --config-channels parameter.
Related: https://postmarketos.org/channels.cfg
Oliver Smith