Add more log fields in 401 Unauthorized requests

What does this MR do and why?

When a user fails to authenticate with a personal access token, previously the log message only showed a 401 status with no details. This commit adds the meta.auth_fail_reason and meta.auth_fail_token_id log fields via the ApplicationContext.

Sample entry:

  "meta.auth_fail_reason": "token_expired",
  "meta.auth_fail_token_id": "PersonalAccessToken/12",

Relates to #464652 (closed)

MR acceptance checklist

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How to set up and validate locally

1. Check out this branch.
2. Go to /-/user_settings/personal_access_tokens and create a new token with read_api.
3. In the Rails console (bin/rails c), change the expiration date to yesterday:

token = PersonalAccessToken.last
token.update!(expires_at: Date.yesterday)

4. Attempt to use this token in the API: curl -H "PRIVATE-TOKEN: <pat>" https://gdk.example.com/api/v4/user
5. Check log/api_json.log. You should see the meta.auth_fail_reason and meta.auth_fail_token_id fields:

  "meta.caller_id": "GET /api/:version/user",
  "meta.remote_ip": "127.0.0.1",
  "meta.feature_category": "user_profile",
  "meta.client_id": "ip/127.0.0.1",
  "meta.auth_fail_reason": "token_expired",
  "meta.auth_fail_token_id": "PersonalAccessToken/12",
  "request_urgency": "low",
  "target_duration_s": 5