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/core/src/main/java/org/elasticsearch/xpack/core/security/SecurityFeatureSetUsage.java
private Map<String, Object> rolesStoreUsage;
    private Map<String, Object> sslUsage;
    private Map<String, Object> tokenServiceUsage;
    private Map<String, Object> apiKeyServiceUsage;
    private Map<String, Object> auditUsage;
    private Map<String, Object> ipFilterUsage;
    private Map<String, Object> anonymousUsage;
    private Map<String, Object> roleMappingStoreUsage;
    private Map<String, Object> fips140Usage;
    private Map<String, Object> operatorPrivilegesUsage;
    private Map<String, Object> domainsUsage;
    public SecurityFeatureSetUsage(StreamInput in) throws IOException {
        super(in);
        realmsUsage = in.readMap();
        rolesStoreUsage = in.readMap();
        sslUsage = in.readMap();
        if (in.getVersion().onOrAfter(Version.V_7_2_0)) {
            tokenServiceUsage = in.readMap();
            apiKeyServiceUsage = in.readMap();
        }
        auditUsage = in.readMap();
        ipFilterUsage = in.readMap();
        anonymousUsage = in.readMap();
        roleMappingStoreUsage = in.readMap();
        if (in.getVersion().onOrAfter(Version.V_7_5_0)) {
            fips140Usage = in.readMap();
        }
        if (in.getVersion().onOrAfter(Version.V_7_11_0)) {
            operatorPrivilegesUsage = in.readMap();
        }