rgw/sts: Adding a configurable rgw_sts_min_session_duration
                                                const string& iamPolicy,
                                                const string& roleArn,
                                                const string& roleSessionName)
 -  : iamPolicy(iamPolicy), roleArn(roleArn), roleSessionName(roleSessionName)
 +  : cct(cct), iamPolicy(iamPolicy), roleArn(roleArn), roleSessionName(roleSessionName)
  {
+   MIN_DURATION_IN_SECS = cct->_conf->rgw_sts_min_session_duration;
    if (duration.empty()) {
      this->duration = DEFAULT_DURATION_IN_SECS;
    } else {
 
    static constexpr uint64_t MAX_ROLE_ARN_SIZE = 2048;
    static constexpr uint64_t MIN_ROLE_SESSION_SIZE = 2;
    static constexpr uint64_t MAX_ROLE_SESSION_SIZE = 64;
+   uint64_t MIN_DURATION_IN_SECS;
    uint64_t MAX_DURATION_IN_SECS;
 +  CephContext* cct;
    uint64_t duration;
    string err_msg;
    string iamPolicy;