redact auth provider secrets in UI
Created by: mollylogue
Under the site configuration page in site-admin, the secrets in the config should display as "REDACTED" rather than the actual secret. I've currently only redacted for open id, github, gitlab, and the executors.accessToken field because those were the obvious ones that jumped out to me, but we can redact others as well if needed.
Closes https://github.com/sourcegraph/sourcegraph/issues/28940