"operation_id" stash variable should be passed to validate_request etc

[karenetheridge]

When declaring routes, extra values can be stuffed into the stash. We might use operation_id to explicitly state which endpoint we want to use in the openapi doc (and if it mismatches the actual request URI, we'll get a validation error).

We may want other stash variables to tweak the configs for the validate cycle, but let's leave that until we figure out what those values might be.

[karenetheridge]

This may only require documentation -- if the stash is set up properly in the route definitions, this should all flow naturally.

[karenetheridge]

Instead of doing this, we should instead try to find the operation using just the URI and method, and then verify that it matches the operation_id stated in the stash (logging a noisy error if there is a mismatch, indicating a problem with the routing).
That allows us to perform validation first, before letting the mojo dispatcher match the routes, so we can return a 405 Method Not Allowed error from validation.