[DOCS] Improvements to contribution guidelines

[lechnerc77]

Based on customer feedback, the following points raise the bar of making a technical contribution to the provider and need improvement in the contribution guideline:

• Recording of test fixtures: The recording of tests via go-vcr is not common for provider development and it should be clearly laid out:
  • What needs to be implemented by the contributor
  • How the fixture is recorded
  • And esp. what is not part of the contribution i.e. should be derived automatically
• Documentation: It is not immediatly clear what documentation needs to be created manually and what gets generated and needs to be part of the contribution. The description of this setp needs to be improved
• Checklist: The checklist needs to made more prominent and also needs an overhaul with regards to clarity in combination with the other points
• PR flow: the PR flow (what checks are running, what do they mean needs to be detailed as this helps contributors undersatnd where there might be action required from their end and where the repository maintainers need to get their hands on.

Some contributors went through reverse engineering things in their first contribution to get the PR through the door, which is a bad experience that we want to avoid with the aforementioned points.