matrix-synapse: route MSC3814 dehydrated-device APIs to workers

Add the unstable MSC3814 dehydrated-device endpoints to both MDAD
worker-routing models:

- the specialized client_reader bucket
- the broad generic_worker route list

This is not a docs-driven change. Current workers.md does not meaningfully
spell out these paths, but the current Synapse code does mount them via the
normal devices servlet registration path, and non-main client workers do not
skip that servlet group.

That makes these endpoints a good fit for the same worker buckets that already
handle the surrounding device- and E2EE-related client APIs.

Refs:
- b99a58719b/docs/workers.md (synapseappgeneric_worker)
- b99a58719b/synapse/rest/client/devices.py (L256-L459)
- b99a58719b/synapse/rest/__init__.py (L81-L129)
- b99a58719b/synapse/rest/__init__.py (L179-L197)

roles/custom/matrix-synapse/vars/main.yml

@@ -39,6 +39,11 @@ matrix_synapse_workers_client_reader_client_server_endpoints:
   - ^/_matrix/client/(api/v1|r0|v3|unstable)/room_keys/
   - ^/_matrix/client/(api/v1|r0|v3|unstable)/keys/(query|changes|claim|room_keys/)
 
+  # MSC3814 dehydrated-device APIs:
+  # Ref: https://github.com/element-hq/synapse/blob/b99a58719b274fcbb327fd8d7649185792bfd12c/synapse/rest/client/devices.py#L256-L459
+  - ^/_matrix/client/unstable/org.matrix.msc3814.v1/dehydrated_device$
+  - ^/_matrix/client/unstable/org.matrix.msc3814.v1/dehydrated_device/[^/]*/events$
+
   # Login, registration, account, and profile APIs
   - ^/_matrix/client/(api/v1|r0|v3|unstable)/login
   - ^/_matrix/client/(api/v1|r0|v3|unstable)/register(/available|/m.login.registration_token/validity|)?
@@ -246,6 +251,10 @@ matrix_synapse_workers_generic_worker_endpoints:
   - ^/_matrix/client/(r0|v3|unstable)/keys/changes$
   - ^/_matrix/client/(r0|v3|unstable)/keys/claim$
   - ^/_matrix/client/(r0|v3|unstable)/room_keys/
+  # MSC3814 dehydrated-device support:
+  # Ref: https://github.com/element-hq/synapse/blob/b99a58719b274fcbb327fd8d7649185792bfd12c/synapse/rest/client/devices.py#L256-L459
+  - ^/_matrix/client/unstable/org.matrix.msc3814.v1/dehydrated_device$
+  - ^/_matrix/client/unstable/org.matrix.msc3814.v1/dehydrated_device/[^/]*/events$
 
   # Registration/login requests
   - ^/_matrix/client/(api/v1|r0|v3|unstable)/login$