Add scheduled sync and build, template for customization of Loop

[marionbarker]

Took @bjornoleh idea from PR #43 and modified it slightly.
Add changes from PR #47 to dev branch (already added to main).

[marionbarker]

Note from April 6, 2023 - posted on zulipchat also.

I am testing this with a special test branch: wip/dev-sync-customize, where I changed targets to point to dev for upstream (instead of main) and to that special test branch (instead of main) in my repo with my own customizations.
This morning, it failed in the auto-update (appropriately) and I got an email that I needed to take action.

It failed because I had changed my testing branch to use a version of Loop not consistent with dev.

Message was:

Failed to merge submodule Loop (not checked out)
CONFLICT (submodule): Merge conflict in Loop
Recursive merging with submodules currently only supports trivial cases.
Please manually handle the merging of each conflicted submodule.

I manually updated the branch to match the expected Loop commit for my special test branch. It should work without errors next time.

[marionbarker]

Note on 11-April-2023

The Auto-update Action (on my special test branch: wip/dev-sync-customize) ran successfully on Mon, 10 Apr 2023 07:00:40 GMT as scheduled. (update.yml)

This branch is similar to the PR with these differences

• It pulls from dev instead of main when looking for new commits
• The branch has some customizations added to build_loop.yml

It correctly reported there were no updates to be pulled from dev.
Next test will be to see if it properly updates for next dev commit when one happens.

[bjornoleh]

Automatic sync by GitHub actions will fail in least two situations:

1. If the update results in a merge conflict, this will have to be resolved manually by command line or similar.

Alternatively, try the manual “Sync fork” in GitHub. If there is a merge conflict, you will be offered the alternative to discard your changes by resetting the branch to the state of the upstream branch.

2. If the update contains changes to GitHub Actions workflow.

GitHub Actions cannot update it’s own workflow file. I am not sure if this is due to a technical limitation, or as a safety feature. In this case, a manual “Sync fork” will work, without the need to discard changes. The next time the sync action will run successfully, provided there are no changes to the workflow(s).

[marionbarker]

On April 20, 2023, I created a LoopWorkspace/patches folder and added two patches to the folder (in my special test branch: wip/dev-sync-customize). That worked as expected - the patches were added when I tested the build from TestFlight.

On April 21, 2023, I needed to manually update that branch because there were non-trivial update and GitHub required me to discard my modifications before it would update. (Therefore, those changes will not show up online at my GitHub username.)

[marionbarker]

Closing this PR since it is based on work from @bjornoleh.(PR #43).