Feature request description

It would be great to show the history of changes made particular to Site Configuration and code host configuration pages in the UI. This would include:

• who made the change
• date/time of the change
• diff

Is your feature request related to a problem? If so, please describe.

This is particularly useful when you spot a change and don't know why/how it was made. In a most recent example, the code host configuration was updated but none of the site administrators remember making the change.

From the administrator in Slack on the benefits of having this history stored in a Git repo:

The benefits we see with having the configs version controlled (either automated or manual) is that we are able to pinpoint when new configs are turned on/off on the instance, which helps a ton in RCAs especially when we conduct different experiments in dev.
Also it helps us see which admin added which config line, which is basically git blame, so that people can be consulted about new changes that they made if we run into any issues later on
One more unintended plus point is that we can share the repo to our users so that they can see which repositories/orgs are in scope in Sourcegraph, and if they want us to add any new repos, they can raise a PR to add it and we can take care of the rest

Additional feedback from the admin in Slack:

Changing admin config should look much like committing to a git repo, where the author, date, time, and commit message are tracked, and history is diff-able.

Describe alternatives you've considered.

Query the database tables directly

Additional context

Requested by: https://github.com/sourcegraph/accounts/issues/6716

Tickets

• https://github.com/sourcegraph/sourcegraph/issues/46031
• https://github.com/sourcegraph/sourcegraph/issues/46032
• Persist edit history for code host configuration, including author, time, diff #46034
• Show edit history for code host configuration on code host page #46035