Add independent credential fields for usage query to support different
query endpoints and authentication methods.
Changes:
- Add `apiKey` and `baseUrl` fields to UsageScript struct
- Remove dependency on provider config credentials in query_usage
- Update test_usage_script to accept independent credential parameters
- Add credential input fields in UsageScriptModal based on template:
* General: apiKey + baseUrl
* NewAPI: baseUrl + accessToken + userId
* Custom: no additional fields (full freedom)
- Auto-clear irrelevant fields when switching templates
- Add i18n text for "credentialsConfig"
Benefits:
- Query API can use different endpoint/key than provider config
- Better separation of concerns
- More flexible for various usage query scenarios