Enable orbit_query_in_rails by default

What does this MR do and why?

Turns the Orbit query flag on by default, so Rails runs Orbit queries unless an instance disables it. The flag was a gitlab_com_derisk type, which can't be default enabled, so it's now a beta flag.

The flag removal MR still needs Workhorse review. This keeps the behavior in 19.6 in the meantime.

On self-managed and Dedicated, this only applies where Orbit is configured (knowledge_graph.enabled). Each Orbit query now holds a Puma thread for as long as it runs. To turn it off, run Feature.disable(:orbit_query_in_rails).

References

• Feature issue: gitlab-org/orbit/knowledge-graph#349 (closed)
• Introduced in !261318 (merged)

How to set up and validate locally

Check Feature.enabled?(:orbit_query_in_rails) with no override. It returns true.

Agent context

• Moved ee/config/feature_flags/gitlab_com_derisk/orbit_query_in_rails.yml to ee/config/feature_flags/beta/, set type: beta and default_enabled: true. The only call site, ee/lib/analytics/knowledge_graph/query_runner.rb, passes no type:, so nothing else changes.
• rollout_issue_url now points to the rollout issue #633423 (closed).
• Not run: specs. The test database isn't set up in this worktree, so the definition and query runner specs couldn't load.