Mark non-essential Orbit endpoints as experimental

What does this MR do and why?

Only the core Orbit endpoints (query, status, skills) are stable enough to keep as Beta. This marks the schema, tools, DSL, format, graph status and agent command endpoints as Experiment, so we can remove them later without rushing. No endpoint is removed.

References

The change is small so it can be backported to the stable branches.

Screenshots or screen recordings

Status of every public /api/v4/orbit/* route:

Route	Before	After
POST /orbit/query	Beta	Beta
POST /orbit/query/:name	Beta	Beta
GET /orbit/query/templates	Beta	Beta
GET /orbit/status	Beta	Beta
GET /orbit/skills	Beta	Beta
GET/HEAD /orbit/skills/:name	Beta	Beta
GET /orbit/skills/:name/*path	Beta	Beta
GET /orbit/schema	Beta	Experiment
GET /orbit/tools	Beta	Experiment
GET /orbit/schema/dsl	none	Experiment
GET /orbit/schema/format	none	Experiment
GET /orbit/graph_status	none	Experiment
GET /orbit/agent/commands	none	Experiment
POST /orbit/agent/commands/:name	none	Experiment
GET /orbit/grep	Experiment	Experiment
POST /orbit/context	Experiment	Experiment

graph_status is marked Experiment here. !264745 (merged) removes it on master later and will rebase over this change.

How to set up and validate locally

1. Run bundle exec rspec ee/spec/requests/api/orbit/data_spec.rb (235 examples pass).

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist.

Agent context

• ee/lib/api/orbit/data.rb: route_setting :lifecycle, :experiment on schema and tools (was :beta) and added on the five unmarked routes. The graph_status line is its own hunk, easy to drop on rebase.
• doc/api/openapi/openapi_v3.yaml: x-gitlab-lifecycle flipped to experiment for schema and tools. The other routes are hidden from the OpenAPI file. doc/api/orbit.md does not document schema or tools, so it is unchanged.
• data_spec.rb: the published routes check now expects context, schema and tools to be experimental and the rest Beta. A new example in the same block checks every hidden route is experimental.
• Verified on Caproni with the full data_spec.rb: 235 examples, 0 failures.