As we are rolling out the user profile feature, we'd like to expand the [Usage API](https://www.elastic.co/guide/en/elasticsearch/reference/current/usage-api.html) to report usage stats of user profiles such as (1) number of enabled user profiles and (2) number of user profiles that are [activated](https://www.elastic.co/guide/en/elasticsearch/reference/current/security-api-activate-user-profile.html) over the past X days. 

Response of the Usage API already contains a `security` field that groups relevant stats from security related features. We expect the new stats for user profiles should be added under it as well, for example:
```
{
  "security: {
    "user_profile": {
      "activated": 78,
      "recently_activated": 42  <1>
    }
  }
}
```
<1> The use of `recently_` is chosen to avoid the field to be tied to a specific time period so it is easier to evolve the definition in future.

x-pack/plugin/security/src/test/java/org/elasticsearch/xpack/security/SecurityInfoTransportActionTests.java
tokenServiceEnabled = randomBoolean();
            settings.put("xpack.security.authc.token.enabled", tokenServiceEnabled);
        } else {
            tokenServiceEnabled = httpSSLEnabled;
        }
        boolean configureEnabledFlagForApiKeyService = randomBoolean();
        final boolean apiKeyServiceEnabled;
        if (configureEnabledFlagForApiKeyService) {
            apiKeyServiceEnabled = randomBoolean();
            settings.put("xpack.security.authc.api_key.enabled", apiKeyServiceEnabled);
        } else {
            apiKeyServiceEnabled = true; 
        }
        final boolean auditingEnabled = randomBoolean();
        settings.put(XPackSettings.AUDIT_ENABLED.getKey(), auditingEnabled);
        final boolean httpIpFilterEnabled = randomBoolean();
        final boolean transportIPFilterEnabled = randomBoolean();
        when(ipFilter.usageStats()).thenReturn(
            MapBuilder.<String, Object>newMapBuilder()
                .put("http", Collections.singletonMap("enabled", httpIpFilterEnabled))
                .put("transport", Collections.singletonMap("enabled", transportIPFilterEnabled))
                .map()
        );
        final boolean rolesStoreEnabled = randomBoolean();
        configureRoleStoreUsage(rolesStoreEnabled);
        final boolean roleMappingStoreEnabled = randomBoolean();
        configureRoleMappingStoreUsage(roleMappingStoreEnabled);
        Map<String, Object> realmsUsageStats = new HashMap<>();
        for (int i = 0; i < 5; i++) {
            Map<String, Object> realmUsage = new HashMap<>();