[#3278] Added configurable PerfMonMgr singleton

[#3278] Added configurable PerfMonMgr singleton

load() now creates PerfMonMgr singleton and invokes it's configure() function.

src/hooks/dhcp/perfmon/monitored_duration.*
    DurationKey::getMessageTypeLabel(uint16_t family, uint16_t msg_type)  - new function
    Translates DHCP_NOTYPE/DHCPV6_NOTYPE to "*"

src/hooks/dhcp/perfmon/perfmon_callouts.cc
    Added PerfMonMgr singleton
    int load(LibraryHandle& handle)  - creates singleton and parses configuration

src/hooks/dhcp/perfmon/perfmon_config.cc
 DurationKeyParser::getMessageNameType4(const std::string& name)
 DurationKeyParser::getMessageNameType6(const std::string& name) - map "*" to NOTYPE
     static std::map<std::string, uint16_t> name_type_map = {

src/hooks/dhcp/perfmon/tests/duration_key_parser_unittests.cc
    TEST_F(DurationKeyParserTest, validScenarios4) - verify "*" message type parses

src/hooks/dhcp/perfmon/libloadtests/load_unload_unittests.cc
    Updated to pass in a valid configuration on load test.