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
if (roleMappingStoreEnabled) {
                    assertThat(source.getValue("role_mapping.native.size"), is(12));
                    assertThat(source.getValue("role_mapping.native.enabled"), is(10));
                } else {
                    final Map<String, Object> roleMapping = source.getValue("role_mapping.native");
                    assertThat(roleMapping.entrySet(), emptyIterable());
                }
                
                assertThat(source.getValue("anonymous.enabled"), is(anonymousEnabled));
                
                assertThat(source.getValue("fips_140.enabled"), is(fips140Enabled));
                
                assertThat(source.getValue("operator_privileges.available"), is(operatorPrivilegesAvailable));
                assertThat(source.getValue("operator_privileges.enabled"), is(operatorPrivilegesEnabled));
            } else {
                if (explicitlyDisabled) {
                    assertThat(source.getValue("ssl"), is(nullValue()));
                } else {
                    assertThat(source.getValue("ssl.http.enabled"), is(httpSSLEnabled));
                    assertThat(source.getValue("ssl.transport.enabled"), is(transportSSLEnabled));
                }
                assertThat(source.getValue("realms"), is(nullValue()));
                assertThat(source.getValue("token_service"), is(nullValue()));
                assertThat(source.getValue("api_key_service"), is(nullValue()));
                assertThat(source.getValue("audit"), is(nullValue()));
                assertThat(source.getValue("anonymous"), is(nullValue()));
                assertThat(source.getValue("ipfilter"), is(nullValue()));
                assertThat(source.getValue("roles"), is(nullValue()));
                assertThat(source.getValue("operator_privileges"), is(nullValue()));