Enhancement: Allow @sourcery-ai-bot to point to forks

[JacobCoffee]

Checklist

• [x] This is a new feature, not a refactoring suggestion
• [x] I have checked for this feature in the Sourcery documentation
• [x] I have checked there are no open requests referencing the same feature

Description

There are Github settings to allow maintainers to have edit rights on forks from the upstream repo. Can @sourcery-ai-bot utilize this capability, and if so can we have it toggleable to allow the PRs @sourcery-ai-bot creates to point back to the fork's branch?

As it stands, when it points to upstream:main instead of the users PR branch on their fork, it is almost useless as 99% of the time the @sourcery-ai-bot PR is just closed.