Add the JSON definitions for the POST, GET, and DELETE endpoints used
to modify client routes. These endpoints are intended for Cloud to
update the `system.client_routes` table.
The API is implemented in `/v2/` because the endpoints process arrays
of objects. Handling of such structures was improved between
Swagger 1.2 and 2.0 versions. There are already similar
`get_metrics_config` and `set_metrics_config` endpoints that operate
on similar structures and they are also in /v2/.
The introduced JSON files start with `, ` but it's intended because
the files are concatenated to the existing (metrics) JSON files,
and they need to represent valid JSON after the concatenation.
Ref: scylladb/scylla-enterprise#5699
70a0418102