apply some fixes and refactor

[oscard0m]

• fix(hasbountylabel): protect from issue.labels possibly undefined
• refactor(fixtures): rename file to issue.opened and use real Payload
• test(types): add JSDocs types to get autocompletion
• fix(comments): verify if the issue has comments or not and get them from API

[oscard0m]

Hey @kaf-lamed-beyt I worked a bit on your code but trying to make your test work.

While setting up the tests to assert your code what is expected I found the following:

• You were relying on issue.comments and you were expecting to be an Array. It's not the case, it's an integer (see /fixtures I attached to see how they look like).
• I added an extra request to retrieve the comments of an issue and iterate over them.
• I've been focusing on the issues.opened handler, I did not check the issue_comment.created but you can take my commits as example and debug that part.

I hope this is useful for you.