chore(meta): Create issue templates and PR template, add authors.md

[simonsan]

To make it easier for the users and us to understand what is happening and why, and what the preconditions are.

The rendered issue form template can be seen here:
https://github.com/rustic-rs/rustic/blob/simonsan-patch-1/.github/ISSUE_TEMPLATE/bug_report.yml

The rendered feature request form template can be seen here:
https://github.com/rustic-rs/rustic/blob/simonsan-patch-1/.github/ISSUE_TEMPLATE/feature_request.yml

Blocked by: Needs adoption to rustic_core extraction to own repository. No choice needed in templates.

[simonsan]

Added note to search our external docs as well, before opening an issue.

[simonsan]

Could you give it a rough look, @aawsome because I'm unsure if the direction is fine? Thanks a lot!

[aawsome]

What about the other (existing) authors which already contributed to the project?

[simonsan]

What about the other (existing) authors which already contributed to the project?

When added, we can open an issue and tag them to please leave their name, would be my proposal. But at some point we might want to start? Better late than never kind of style

[simonsan]

What about the other (existing) authors which already contributed to the project?

Note for us (taken from git-cliff): A list of contributors can be derived using curl -s https://api.github.com/repos/orhun/git-cliff/contributors | jq -r .[].login | xargs -I {} echo "- [ ] @{}"