[5680] kea-dhcp4 supports client FQDN name sanitizing

[5680] kea-dhcp4 supports client FQDN name sanitizing

src/lib/dhcpsrv/d2_client_mgr.h
    D2ClientMgr::adjustDomainName() - added logic to
    sanitize the inbound FQDN name when configured to do so

src/lib/dhcpsrv/tests/d2_client_unittest.cc
    TEST(D2ClientMgr, sanitizeFqdnV4)
    TEST(D2ClientMgr, sanitizeFqdnV6) - new tests

src/bin/dhcp4/tests/fqdn_unittest.cc
    TEST_F(NameDhcpv4SrvTest, sanitizeFqdn) - new test