ci: Fix automodel and submodule check comments from a fork

[chtruong814]

What does this PR do ?

Fix automodel and submodule check comments from a fork

When a PR is made from a fork, the PR comment job does not have the right permissions to write to the PR due to security reasons. We can enable this by separating the PR comment steps to separate jobs that run on the pull_request_target event. When a job runs in the context of that event (as opposed to the typical pull_request event), it runs from the perspective off the base branch and has the permissions to write to the PR such as adding a comment.

https://docs.github.com/en/actions/reference/workflows-and-actions/events-that-trigger-workflows#pull_request_target

Because of the increased privilege that the fork PR would have, it is not recommended to check out and do anything with the code from the PR itself. So, we only do the commenting with the pull_request_target event. To clarify:

1. On pull_request the automodel and submodule checks happen as usual and write their comments to a Github artifact
2. On pull_request_target the corresponding jobs poll for the artifacts to exist. If the artifacts do not exist, then nothing fails. If they do exist within a given number of tries, then it will comment on the PR.

Here's an example of this working:
chtruong814#3

Those comments are from a PR I made from my personal Github username to a fork of RL.

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[terrykong]

@ko3n1g to review