Add table and model for error tracking settings

What does this MR do?

This MR adds the DB migration (adds table error_tracking_settings) and new model (ErrorTracking::ProjectErrorTrackingSetting) for holding Sentry settings. It is part of the issue to list sentry errors within GitLab.

This MR only contains the DB migration and model in order to keep the MR small.

There will be further MRs with controllers, services, etc.

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/55178

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer