Changes to the review process with git migration

[jennyhickson]

Dear All,

Following on from #510, another of the changes that you will notice as we move to GitHub is the review process.

We will continue to have a two stage review (SciTech followed by Code) as we did in Trac and in order to facilitate this we are using a GitHub project to track pull requests through the review stages. Every pull request will be automatically added to the project and you'll find a box with review details gets added to the pull request side bar. There will also be space in the pull request description to document who is doing each review.

The pull request and review process is documented in the working practices. In summary:

1. The developer should organise a SciTech review, document who it is in the pull request description (and optionally in the project), and request their review.
2. Open (non-draft) pull requests will have a code reviewer assigned to them by the SSD team. We will regularly check for new PRs, but if you think you've been overlooked then get in touch.
3. Once the SciTech review has been completed, either the SciTech reviewer or the developer should add the assigned code reviewer to the reviewers list. If they are already there (perhaps because they are also a code owner), then message them in a comment to let them know. Change the state in the project box to Code Review.
4. As the code review process nears completion the developer should update their branch with the latest changes from Main and ensure that testing is still valid. Please don't do this before this point.
5. Once the code review has also been completed the state can be changed to Approved - this is useful if there is a delay before commit.
6. The Code Reviewer will finalise any upgrade macros, KGO updates and linked changes as well as running any final testing before merging the change to Main. 

Many Thanks
Jenny