workhorse: Return 400 from /cable without valid websocket upgrade

What does this MR do and why?

workhorse: Return 400 from /cable without valid websocket upgrade

Previously, a request to /cable without a valid websocket upgrade would return a 500 because wsRoute requires websocket headers to match the route. This results in a confusing error response and logs. Implement a new method wsRouteStrict that matches the route regardless of headers so an informative error can be returned.

References

Resolves #583200 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Compile & restart workhorse
2. Navigate to a page that uses websockets (like the merge requests page)
3. In your dev tools network tab, filter by Socket, and verify that the connection successfully upgraded (status 101)
4. curl -i http://localhost:3000/-/cable returns a 400 with websocket upgrade required

MR acceptance checklist

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