Move eng-apps-devex to OWNERTEAMS for approval resolution

[simonfaltum]

Why

The maintainer-approval workflow uses @databricks/eng-apps-devex team references in OWNERS, then calls teams.getMembershipForUserInOrg() to check if a reviewer belongs to that team. This API requires read:org scope, which GITHUB_TOKEN doesn't support (it only has repository-scoped permissions). The API returns 404 for privacy reasons, the code silently treats that as "not a member", and team-based approvals never resolve.

This showed up on #4968 where arsenyinfo (a member of eng-apps-devex) approved, but the check stayed pending until a maintainer stepped in.

Changes

We already have an OWNERTEAMS mechanism that expands team:<name> references to individual logins at parse time, no API calls needed. team:bundle and team:platform already use it. This PR adds team:eng-apps-devex to the same system:

• OWNERTEAMS: added team:eng-apps-devex with the full team roster (12 members)
• OWNERS: replaced all @databricks/eng-apps-devex references with team:eng-apps-devex
• Tests: updated to use OWNERTEAMS-based team resolution instead of mocking the GitHub API

Test plan

• All 20 existing maintainer-approval tests pass
• Team member approval now resolves via OWNERTEAMS expansion (no API dependency)
• Non-team-member approval correctly stays pending
• make ws passes

This pull request was AI-assisted by Isaac.