Add o11y_oauth_application_id to application_settings
What does this MR do?
Adds a nullable o11y_oauth_application_id column to application_settings. The add_column migration is a regular schema migration (required for add_column operations); the concurrent index and concurrent foreign key to oauth_applications (ON DELETE SET NULL) are post-deployment migrations, per GitLab convention for index/FK additions on an existing column.
Also adds the config/application_setting_columns/o11y_oauth_application_id.yml definition file required by the ensure-application-settings-have-definition-file CI check.
This column will hold the ID of the shared GitLab OAuth application used to mint per-user SigNoz backend-for-frontend (BFF) sessions.
This is the first of a stack of MRs splitting up the observability BFF session broker feature by layer (database → settings/config → backend → frontend). No code reads or writes this column yet -- it is intentionally split out on its own so the schema change can be reviewed and merged independently of the feature code that will use it.
References
- gitlab-org/embody-team/experimental-observability/documentation#101
- gitlab-org/embody-team/experimental-observability/documentation#163 — local dev setup guide for this feature
MR acceptance checklist
This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.