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/main/java/org/elasticsearch/xpack/security/Security.java
new ActionHandler<>(ChangePasswordAction.INSTANCE, TransportChangePasswordAction.class),
            new ActionHandler<>(AuthenticateAction.INSTANCE, TransportAuthenticateAction.class),
            new ActionHandler<>(SetEnabledAction.INSTANCE, TransportSetEnabledAction.class),
            new ActionHandler<>(HasPrivilegesAction.INSTANCE, TransportHasPrivilegesAction.class),
            new ActionHandler<>(GetUserPrivilegesAction.INSTANCE, TransportGetUserPrivilegesAction.class),
            new ActionHandler<>(GetRoleMappingsAction.INSTANCE, TransportGetRoleMappingsAction.class),
            new ActionHandler<>(PutRoleMappingAction.INSTANCE, TransportPutRoleMappingAction.class),
            new ActionHandler<>(DeleteRoleMappingAction.INSTANCE, TransportDeleteRoleMappingAction.class),
            new ActionHandler<>(CreateTokenAction.INSTANCE, TransportCreateTokenAction.class),
            new ActionHandler<>(InvalidateTokenAction.INSTANCE, TransportInvalidateTokenAction.class),
            new ActionHandler<>(GetCertificateInfoAction.INSTANCE, TransportGetCertificateInfoAction.class),
            new ActionHandler<>(RefreshTokenAction.INSTANCE, TransportRefreshTokenAction.class),
            new ActionHandler<>(SamlPrepareAuthenticationAction.INSTANCE, TransportSamlPrepareAuthenticationAction.class),
            new ActionHandler<>(SamlAuthenticateAction.INSTANCE, TransportSamlAuthenticateAction.class),
            new ActionHandler<>(SamlLogoutAction.INSTANCE, TransportSamlLogoutAction.class),
            new ActionHandler<>(SamlInvalidateSessionAction.INSTANCE, TransportSamlInvalidateSessionAction.class),
            new ActionHandler<>(SamlCompleteLogoutAction.INSTANCE, TransportSamlCompleteLogoutAction.class),
            new ActionHandler<>(SamlSpMetadataAction.INSTANCE, TransportSamlSpMetadataAction.class),
            new ActionHandler<>(OpenIdConnectPrepareAuthenticationAction.INSTANCE, TransportOpenIdConnectPrepareAuthenticationAction.class),
            new ActionHandler<>(OpenIdConnectAuthenticateAction.INSTANCE, TransportOpenIdConnectAuthenticateAction.class),
            new ActionHandler<>(OpenIdConnectLogoutAction.INSTANCE, TransportOpenIdConnectLogoutAction.class),
            new ActionHandler<>(GetBuiltinPrivilegesAction.INSTANCE, TransportGetBuiltinPrivilegesAction.class),
            new ActionHandler<>(GetPrivilegesAction.INSTANCE, TransportGetPrivilegesAction.class),
            new ActionHandler<>(PutPrivilegesAction.INSTANCE, TransportPutPrivilegesAction.class),
            new ActionHandler<>(DeletePrivilegesAction.INSTANCE, TransportDeletePrivilegesAction.class),
            new ActionHandler<>(CreateApiKeyAction.INSTANCE, TransportCreateApiKeyAction.class),
            new ActionHandler<>(GrantApiKeyAction.INSTANCE, TransportGrantApiKeyAction.class),
            new ActionHandler<>(InvalidateApiKeyAction.INSTANCE, TransportInvalidateApiKeyAction.class),
            new ActionHandler<>(GetApiKeyAction.INSTANCE, TransportGetApiKeyAction.class),
            new ActionHandler<>(QueryApiKeyAction.INSTANCE, TransportQueryApiKeyAction.class),