Enable Bors to process commands from PR description when opened

[mostafa630]

This PR introduces a new functionality by using process_pr_description_commands that allows commands written in the PR description to be processed in the same way as regular pull request comments.

• added create_pr_description_comment to convert a PR description into a PullRequestComment
• reuse the existing handle_comment function
• updated handle_pull_request_opened signature to include ctx: Arc<BorsContext> and merge_queue_tx: MergeQueueSender because handle_comment function needs them.
• call the process_pr_description_commands inside the handle_pull_request_opened
• Add process_bors_commands_in_pr_description test

[Kobzol]

Hi, thanks for the PR! I thought that we'd generate the PR comment in the webhook handler itself, so that the rest of the codebase doesn't even know about where the comment is coming from, but this also works.

Could you please add a test for this? You can copy-paste enqueue_prs_on_pr_opened, and in the open_pr closure, set something to the PR's description (e.g. start a try build or set the PR's priority), and then check that bors reacted to it. You can check other tests for examples, look for @bors commands in them.

[mostafa630]

@Kobzol
I’ve added the test function process_bors_commands_in_pr_description and it works as expected

If I understand correctly, instead of adding the logic in pr_event.rs, we could move it to handler/mod.rs and call it after the handle_pull_request_opened(....) function call:

BorsRepositoryEvent::PullRequestOpened(payload) {
    ..............
    handle_pull_request_opened(......)
    process_pr_description_commands(....)
}

This approach for sure would leave pr_event.rs unchanged just the added test ,so if that what you need I can do it for sure

[Kobzol]

I was more thinking about generating two events per opened PR in the webhook code, but it would needlessly complicate the code for a single use-case, your solution is fine. And the test looks good, thank you!

[mostafa630]

@Kobzol
Thank you for reviewing and merging , I appreciate your time and feedback.