Create a unique launch agent for each architecture

[lkrms]

Apologies for the double-up; #62 was based on my master branch and I was hoping the PR would follow when I renamed it while rebasing on the upstream master. Lesson learned: always branch before opening a PR! The original description follows.

On an Apple Silicon system with 2 Homebrew installations (at /opt/homebrew and /usr/local for arm64 and x86_64 respectively), arch --x86_64 /usr/local/bin/brew autoupdate subcommand conflicts with /opt/homebrew/bin/brew autoupdate subcommand, which makes it impossible to enable autoupdate for both installations simultaneously.

The workaround I've used here may not be suitable for wider adoption, but hopefully a few revisions will get it there if not.

TL;DR:

• the LaunchAgent's name now includes the applicable architecture (e.g. com.github.domt4.homebrew-autoupdate.arm64)
• the previous name is kept if ~/Library/LaunchAgents/com.github.domt4.homebrew-autoupdate.plist already exists (the new name only takes effect after brew autoupdate delete)
• ~/Library/Logs/com.github.domt4.homebrew-autoupdate/ isn't deleted unless it's empty

There are probably things I've missed, but it seems to be working as expected here (although I don't have --upgrade enabled).

[github-actions[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[lkrms]

FYI @DomT4, I've just rebased and cleaned up this branch, with a couple of improvements:

• the notifier now reads from the log file associated with the instance raising the notification (NB: the updated app is currently unsigned), and
• at runtime, brew update etc. are now invoked using the same architecture brew autoupdate was originally called with

The changes haven't come through because this PR is closed, but I assume you can remedy that? Let me know if you'd like me to open another PR. You can check out the branch here if needed.