Advertise "users-admin" service

The users management portal can be discovered like other services and
if its settings are added, or changed the `service-users-admin-changed`
event is raised.

README.md

@@ -95,6 +95,16 @@ For instance:
 
     https://<node FQDN>/users-admin/domain.test/
 
+The backend endpoint is advertised as `users-admin` service and can be
+discovered in the usual ways, as documented in [Service
+discovery](https://nethserver.github.io/ns8-core/modules/service_providers/#service-discovery).
+For instance:
+
+    api-cli run module/mymodule1/list-service-providers  --data '{"service":"users-admin", "filter":{"domain":"dp.nethserver.net","node":"1"}}'
+
+The event `service-users-admin-changed` is raised when the serivice
+becomes available or is changed.
+
 The backend of the module runs under the `api-moduled.service` Systemd
 unit supervision. Refer also to `api-moduled` documentation, provided by
 `ns8-core` repository.

imageroot/actions/configure-module/80start_amld

@@ -11,7 +11,12 @@ import sys
 import os
 import string
 import secrets
+import json
 
+agent_id = os.environ['AGENT_ID']
+node_id = int(os.environ['NODE_ID'])
+domain = os.environ['LDAP_DOMAIN']
+ip_address = os.environ['LDAP_IPADDR']
 
 _, amld_port, _ = (os.environ['TCP_PORTS'] + ',,').split(",", 2)
 
@@ -41,4 +46,22 @@ response = agent.tasks.run(
     },
 )
 
+# Add the `users-admin` service discovery information, and advertise this
+# new service instance:
+rdb = agent.redis_connect(privileged=True)
+trx = rdb.pipeline()
+trx.delete(agent_id + '/srv/http/users-admin')
+trx.hset(agent_id + '/srv/http/users-admin', mapping={
+    "port": amld_port,
+    "url": f"http://{ip_address}:{amld_port}",
+    "domain": domain,
+    "node": node_id,
+})
+trx.publish(agent_id + '/event/service-users-admin-changed', json.dumps({
+    'domain': domain,
+    'node': node_id,
+    'key': agent_id + '/srv/http/users-admin',
+}))
+trx.execute()
+
 agent.run_helper("systemctl", "-T", "--user", "enable", "--now", "api-moduled.service")

imageroot/actions/import-module/80start_amld

@@ -0,0 +1 @@
+../configure-module/80start_amld

imageroot/actions/restore-module/80start_amld

@@ -0,0 +1 @@
+../configure-module/80start_amld