Revise issue/pr acceptance process and update documentation

[jmcook1186]

Sub of #657

User story

As a contributor I want to know the steps that will be taken to evaluate my PR/issue in advance so my expectations are set. As a core developer, I want to have a clear process for issue/pr handling so that I can be confident I am handlign them all consistently, efficiently and fairly.

Rationale

The QA epic is the right time to introspect on our issue/pr processes. We have made progress on theis recently but we want to come out of this epic confident we have processes that will serve us for the long term and won't become bottlenecks as we scale.

Implementation details

• examine our current processes
• propose any changes in writing
• discuss changes with team
• update contribution guidelines and internal process docs accordingly

Priority

4/5

Size

M

What does "done" look like?

Processes either re-affirmed or updated. Documentation updated if needed.

Deadline

tbc