feat: Add tweet preview and tweeted URL to PR conversation

[IstoraMandiri]

Fixes #223

After each PR preview generation, the bot will post a comment to the PR thread, making things far more obvious for contributors and maintainers.

Example: IstoraMandiri/twitter-together-testing#18

EDIT: In draft mode until I implement post-merge URL tweeting and remote fork PRs.

TODO: Document updating workflow, gituhb for "Actions permissions", splitting workflow into two files

[IstoraMandiri]

@gr2m Perhaps you can point me in the right direction with the post-merge part of this PR with your better knowledge of github actions and octokit.

Currently the push action will add a comment of the tweeted URL to the commit itself, but this is not very visible and I would like to have it also post a link to the published tweet in the conversation thread of the merged PR.

The problem is that within the push action, I cannot find a reference to the pull request number anywhere in the GITHUB_EVENT_PATH payload. Is there some other way to get a reference to the PR that triggered the push action so I can then post in that thread?

Thanks.

[IstoraMandiri]

Another problem I've run into is that the pull_request action does not have permissions to post a comment if the PR is coming from a forked repo.

I think we'd somehow need to use pull_request_target, or otherwise grant permissions. Any suggestions @gr2m ?

[gr2m]

I think we'd somehow need to use pull_request_target

That is true. When using Actions, that's what we need to do. We could support both and tell if folks are uncomfortable to use the pull_request_target trigger, they can use pull_request but won't get comment previews. We can also narrow down the permission of the passed GITHUB_TOKEN to only what we need.

I think we'll need to update action code to account for the event trigger change

[IstoraMandiri]

I'm closing this PR and integrating it into #224