Cron job to regularly check and bump for updates to Ghidra HEAD

[ekilmer]

Related to changes made in #15

I think some sort of bot or GitHub Action would be the best way to keep track of new commits made to Ghidra's default branch (master). Sort of like Dependabot but we would have to script it ourselves. I see the workflow like:

1. Create a weekly GitHub Action cron job
2. Grab the latest commit from default development Ghidra branch (master)
3. Run some checks for updates and make the necessary source code changes (see below for what should be included)
4. If changes, create new branch, commit and push as new PR to GitHub
5. Let CI run on created PR
6. Wait for manual approval/changes

Checks for "updates":

• New commit to HEAD of Ghidra master branch and update the src/setup-ghidra-source.cmake file/line
• Automatically update the listing of slaspec files with some find . -name "*.slaspec" magic
• Check and report in PR details if any files have been added to some monitored directories (removed files will almost certainly cause compilation errors and be caught by CI)

The cron-job action should ideally be runnable locally as well.

Originally discussed by @ekilmer in #15 (comment)