docs(contributing): add guidelines for members and contributors

[AnonymousWP]

Describe the documentation you want to change

To reach consistency and transparency, we'd like to setup some rules users (both members of this organisation and contributors) should stick to. Examples of this are:

• Conventional Commits
• A checklist of steps we need to perform before pushing a new tag (and thus release)
• Closing issues after a certain time period, e.g. after 1 month of inactivity. This could be automated as well where a webhook/bot notifies us if an issue has been stale for a month. Based on the context of the issue, we decide whether we close the issue or not.

Acknowledgements

• This issue is not a duplicate of an existing documentation change request.
• I have chosen an appropriate title.
• All requested information has been provided properly.