matrix-tuwunel: add Tuwunel homeserver role (#5200)

Tuwunel is a Matrix homeserver maintained by the matrix-construct
organisation. See https://matrix-construct.github.io/tuwunel/.

The rendered TOML emits only keys exposed as Ansible variables; the
rest fall back to tuwunel's upstream defaults. Anything not surfaced
can be set via the TUWUNEL_* env extension or by overriding the
template path.

Popular features Tuwunel adds variables for:

- OAuth2/OIDC identity providers (a list of `[[global.identity_provider]]`
  blocks; brand-aware defaults for Google, GitHub, Keycloak, MAS, etc)
- LDAP and JWT authentication
- Media storage providers (native local and S3 with multipart upload)
- RocksDB tuning (compression, direct_io, parallelism, online backups)
- Native TLS dual-protocol mode
- Blurhashing, Sentry crash reporting

Auto-wired from existing playbook globals: well-known client URL,
TURN/coturn, MatrixRTC LiveKit URL, federation.

The `tuwunel-migrate-from-conduwuit` tag performs a binary-swap
migration. Migration from any other Conduit derivative is unsupported
and would corrupt the database.

Signed-off-by: Jason Volk <jason@zemos.net>

roles/custom/matrix-base/tasks/validate_config.yml

@@ -13,7 +13,7 @@
 - name: Fail if invalid homeserver implementation
   ansible.builtin.fail:
     msg: "You need to set a valid homeserver implementation in `matrix_homeserver_implementation`"
-  when: "matrix_homeserver_implementation not in ['synapse', 'dendrite', 'conduit', 'continuwuity']"
+  when: "matrix_homeserver_implementation not in ['synapse', 'dendrite', 'conduit', 'continuwuity', 'tuwunel']"
 
 - name: (Deprecation) Catch and report renamed settings
   ansible.builtin.fail: