collab: Add ability to revoke LLM service access tokens (#16143)

This PR adds the ability to revoke access tokens for the LLM service.

There is a new `revoked_access_tokens` table that contains the
identifiers (`jti`) of revoked access tokens.

To revoke an access token, insert a record into this table:

```sql
insert into revoked_access_tokens (jti) values ('1e887b9e-37f5-49e8-8feb-3274e5a86b67');
```

We now attach the `jti` as `authn.jti` to the tracing spans so that we
can associate an access token with a given request to the LLM service.

Release Notes:

- N/A

crates/collab/src/main.rs

@@ -150,6 +150,7 @@ async fn main() -> Result<()> {
                             "http_request",
                             method = ?request.method(),
                             matched_path,
+                            authn.jti = tracing::field::Empty
                         )
                     })
                     .on_response(