Create templates for issues and pull requests

[hoegertn]

It would be great to have templates for issues and pull requests. Ideas can be borrowed from the CDK project.

Issues:

• several types for bugs, features, chores
• Call to action for community to take issues

PRs:

• checklist for contributors
• checklist for reviewers and maintainers
• information for correct PR titles

[dbartholomae]

I've researched a bit around this when setting up https://github.com/dbartholomae/lambda-middleware and preparing for Hacktoberfest a few years ago. Here's the Issue templates I ended up with: https://github.com/dbartholomae/lambda-middleware/tree/main/.github/ISSUE_TEMPLATE

I'll open a PR shortly to add them here so we can discuss in the PR whether they work, as well as any changes needed.