Display org secrets read-only on repo secrets settings page

[delvh]

Inside the repo secrets settings, it would be a good idea to display the user/org secrets to show what secrets will override another secret and which won't.
However, they should not be modifiable (so read-only, doesn't even need to display the value), and instead we could link to the corresponding settings page on a click.

Originally posted by @delvh in #22142 (comment)