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
}
    @Override
    protected void innerXContent(XContentBuilder builder, Params params) throws IOException {
        super.innerXContent(builder, params);
        if (enabled) {
            builder.field(REALMS_XFIELD, realmsUsage);
            builder.field(ROLES_XFIELD, rolesStoreUsage);
            builder.field(ROLE_MAPPING_XFIELD, roleMappingStoreUsage);
            builder.field(SSL_XFIELD, sslUsage);
            builder.field(TOKEN_SERVICE_XFIELD, tokenServiceUsage);
            builder.field(API_KEY_SERVICE_XFIELD, apiKeyServiceUsage);
            builder.field(AUDIT_XFIELD, auditUsage);
            builder.field(IP_FILTER_XFIELD, ipFilterUsage);
            builder.field(ANONYMOUS_XFIELD, anonymousUsage);
            builder.field(FIPS_140_XFIELD, fips140Usage);
            builder.field(OPERATOR_PRIVILEGES_XFIELD, operatorPrivilegesUsage);
            if (domainsUsage != null && false == domainsUsage.isEmpty()) {
                builder.field(DOMAINS_XFIELD, domainsUsage);
            }
        } else if (sslUsage.isEmpty() == false) {
            
            
            builder.field(SSL_XFIELD, sslUsage);
        }
    }
    public Map<String, Object> getRealmsUsage() {
        return Collections.unmodifiableMap(realmsUsage);
    }
}