Add various polish to Conduwuit

https://github.com/Virkkunen and I have been working on the same feature
simultaneously.

This patch adds my additional independent work on top of his changes.

Notable changes here compared to Virkkunen's original work:

- renaming config-related variables (`matrix_conduwuit_*` ->
  `matrix_conduwuit_config_*`). This is consistent with other roles (and
  better), but deviates from how the Conduit role was implemented.

- using a full configuration sample from https://conduwuit.puppyirl.gay/configuration.html
  instead of using the old Conduit config file template

- introducing configurability for more Conduwuit config settings, to support easy registration, etc.

- removing configuration settings that Conduwuit does not support
  anymore (e.g. `max_concurrent_requests`)

- cross-linking docs pages for Conduit and Conduwuit

- a Conduwuit docs page which is much improved compared to the old
  Conduit one

- REAMDE updates

group_vars/matrix_servers

@@ -553,7 +553,7 @@ matrix_homeserver_container_client_api_endpoint: |-
       'synapse': ('matrix-synapse-reverse-proxy-companion:8008' if matrix_synapse_reverse_proxy_companion_enabled | default(false) else ('matrix-synapse:'+ matrix_synapse_container_client_api_port | default('8008') | string)),
       'dendrite': ('matrix-dendrite:' + matrix_dendrite_http_bind_port | default('8008') | string),
       'conduit': ('matrix-conduit:' + matrix_conduit_port_number | default('8008') | string),
-      'conduwuit': ('matrix-conduwuit:' + matrix_conduwuit_port_number | default('8008') | string),
+      'conduwuit': ('matrix-conduwuit:' + matrix_conduwuit_config_port_number | default('8008') | string),
     }[matrix_homeserver_implementation]
   }}
 
@@ -563,7 +563,7 @@ matrix_homeserver_container_federation_api_endpoint: |-
       'synapse': ('matrix-synapse-reverse-proxy-companion:8048' if matrix_synapse_reverse_proxy_companion_enabled else ('matrix-synapse:'+ matrix_synapse_container_federation_api_plain_port | default('8008') | string)),
       'dendrite': ('matrix-dendrite:' + matrix_dendrite_http_bind_port | default('8008') | string),
       'conduit': ('matrix-conduit:' + matrix_conduit_port_number | default('8008') | string),
-      'conduwuit': ('matrix-conduwuit:' + matrix_conduwuit_port_number | default('8008') | string),
+      'conduwuit': ('matrix-conduwuit:' + matrix_conduwuit_config_port_number | default('8008') | string),
     }[matrix_homeserver_implementation]
   }}
 
@@ -5818,7 +5818,7 @@ matrix_conduwuit_enabled: "{{ matrix_homeserver_implementation == 'conduwuit' }}
 
 matrix_conduwuit_hostname: "{{ matrix_server_fqn_matrix }}"
 
-matrix_conduwuit_allow_federation: "{{ matrix_homeserver_federation_enabled }}"
+matrix_conduwuit_config_allow_federation: "{{ matrix_homeserver_federation_enabled }}"
 
 matrix_conduwuit_container_network: "{{ matrix_homeserver_container_network }}"
 
@@ -5844,7 +5844,7 @@ matrix_conduwuit_container_labels_public_federation_api_traefik_tls: "{{ matrix_
 matrix_conduwuit_container_labels_internal_client_api_enabled: "{{ matrix_playbook_internal_matrix_client_api_traefik_entrypoint_enabled }}"
 matrix_conduwuit_container_labels_internal_client_api_traefik_entrypoints: "{{ matrix_playbook_internal_matrix_client_api_traefik_entrypoint_name }}"
 
-matrix_conduwuit_turn_uris: |
+matrix_conduwuit_config_turn_uris: |
   {{
     ([
       'turns:' + matrix_server_fqn_matrix + '?transport=udp',
@@ -5857,9 +5857,11 @@ matrix_conduwuit_turn_uris: |
     ] if matrix_coturn_enabled else [])
   }}
 
-matrix_conduwuit_turn_secret: "{{ matrix_coturn_turn_static_auth_secret if (matrix_coturn_enabled and matrix_coturn_authentication_method == 'auth-secret') else '' }}"
-matrix_conduwuit_turn_username: "{{ matrix_coturn_lt_cred_mech_username if (matrix_coturn_enabled and matrix_coturn_authentication_method == 'lt-cred-mech') else '' }}"
-matrix_conduwuit_turn_password: "{{ matrix_coturn_lt_cred_mech_password if (matrix_coturn_enabled and matrix_coturn_authentication_method == 'lt-cred-mech') else '' }}"
+matrix_conduwuit_config_turn_secret: "{{ matrix_coturn_turn_static_auth_secret if (matrix_coturn_enabled and matrix_coturn_authentication_method == 'auth-secret') else '' }}"
+matrix_conduwuit_config_turn_username: "{{ matrix_coturn_lt_cred_mech_username if (matrix_coturn_enabled and matrix_coturn_authentication_method == 'lt-cred-mech') else '' }}"
+matrix_conduwuit_config_turn_password: "{{ matrix_coturn_lt_cred_mech_password if (matrix_coturn_enabled and matrix_coturn_authentication_method == 'lt-cred-mech') else '' }}"
+
+matrix_conduwuit_self_check_validate_certificates: "{{ matrix_playbook_ssl_enabled }}"
 
 ######################################################################
 #