Create bot for keeping track of PRs opened by the Community

[varsill]

Open PRs can be obtained from e.g.: https://github.com/pulls?q=is%3Aopen+is%3Apr+archived%3Afalse+org%3Amembraneframework+-author%3ANoarkhh

[varsill]

Repository with code artifacts: https://github.com/membraneframework-labs/pull_requests_bot