fix(orbit): deprecate the methods whose endpoints GitLab removed

What does this MR do?

GitLab 19.6 removed the five Orbit REST routes these methods call, and GitLab.com already answers 404 Not Found for each. This MR deprecates the methods, names what each removal MR offers in their place, and keeps them until v4.0:

Method	Removed route	Replacement	Removed by
GetStatus	GET /orbit/status	GraphQL Query.orbit.serviceStatus	gitlab-org/gitlab!265633 (merged)
GetSchema	GET /orbit/schema	GraphQL Query.orbit.schema	gitlab-org/gitlab!265633 (merged)
GetGraphStatus	GET /orbit/graph_status	GraphQL Group.orbit and Project.orbit (indexing, itemCounts)	gitlab-org/gitlab!264745 (merged)
GetTools	GET /orbit/tools	MCP tools/list on POST /api/v4/orbit/mcp	gitlab-org/gitlab!265998 (merged)
GetDsl	GET /orbit/schema/dsl	None: the JSON query DSL is gone, queries are Orbit query language text	gitlab-org/gitlab!261947 (merged)

The 20 option and response types only these methods use are deprecated too.

Query and QueryRaw still work, but their docs described a JSON query object, which POST /orbit/query now refuses with 400. They now describe query language text and link the current anchor, #run-a-query.

!3089 (merged) (open) edits the GetStatus doc links next to two of these paragraphs, so the second of the two to merge needs a small rebase. If !3089 (merged) merges first, I will rebase this one.

Is this a breaking change?

No. Only doc comments change: nothing is removed, and callers get a staticcheck SA1019 warning.

How was this tested?

• make generate and make fmt change no file, and make lint (golangci-lint 2.15.0, buf) and make test pass on Go 1.27.3. make test also passes on Go 1.26.10.
• A caller module gets SA1019 from staticcheck on each of the five methods and 20 types, and none on Query, QueryRaw or their types.
• On GitLab.com on 2026-10-29 the five routes answered 404 {"error":"404 Not Found"}, and POST /orbit/query answered 400 to a JSON query object and 200 to query language text.

I found this while moving the Orbit tools of gitlab-mcp-server, which is built on this library, off the removed routes.