Temporal default .github files

Temporal's default community health files. See docs: https://docs.github.com/en/github/building-a-strong-community/creating-a-default-community-health-file

What is this

This is the default file for all Temporal OSS repos. Primarily we offer:

• 2 basic issue templates, covering Bug Report and Feature Requests
• 1 PR template, reminding the contributor to file an issue first
• in future, we may add CONTRIBUTING.md and SECURITY.md

Why do this

The goal of this is to make a small nudge to improve our OSS community submissions, and set public expectations on PRs.

Internal instructions

To Temporal employees: You can override this behavior on a per-repo basis, simply by making another file with the same names in side of your repo. More details in GitHub's docs.

You can also improve your issue triage by using saved replies to close issues with a polite and reasonable tone.

Acknowledgements

Thanks to https://github.com/stevemao/github-issue-templates for our base templates.