feat: Add stalebot to help with PRs/Issues

[schristoff]

Is your feature request related to a problem? Please describe.
It would be useful to have a couple more helpers around to help with day to day maintenance and monitoring of issues & PRs in Porter. Stalebot could help us keep our focus on current issues and ping us on PRs that we may have forgotten about.

Describe the solution you'd like
Implement Stalebot but in a sustainable way. Certain tags on PRs should be ignored (ex: pep003, or perhaps any pep tag?, docs should be ignored)
It will take some discussion and fine tuning to find exactly the best way it works in our community.

[sbdtu5498]

I will take care of it. I am currently working on something that can help solve this problem in the wider CNCF community. Those sets of GitHub actions fit the description so you can use some of those as per your requirements. Though it is not yet complete, but would be available soon.

[AGMETEOR]

@sbdtu5498 is it ok if I take this off your plate?
cc: @schristoff

[sbdtu5498]

@AGMETEOR Sure you can go ahead and add something if you have. I am working on a general template anyways. So once it would be done. I can also be integrated apart. But if you want to work on it right now, please go ahead.

[AGMETEOR]

Alright. Thanks.

[AGMETEOR]

Hey @schristoff could I get assigned this issue? Also, in case you need help with managing community issues, I have some free time now.

[sbdtu5498]

You can start working on this one, I think it's alright even if it is not assigned.