[5680] kea-dhcp4/6 now parse hostname-char-set and hostname-char-replacment params

[5680] kea-dhcp4/6 now parse hostname-char-set and hostname-char-replacment params

Added to parsing and parsing unit tests.
Servers do not yet utilize the values.

Modified:

src/bin/dhcp4/dhcp4_lexer.ll
src/bin/dhcp4/dhcp4_parser.yy

src/bin/dhcp4/tests/config_parser_unittest.cc
src/bin/dhcp4/tests/fqdn_unittest.cc
src/bin/dhcp4/tests/get_config_unittest.

src/bin/dhcp6/dhcp6_lexer.ll
src/bin/dhcp6/dhcp6_parser.yy

src/bin/dhcp6/tests/config_parser_unittest.cc
src/bin/dhcp6/tests/fqdn_unittest.cc
src/bin/dhcp6/tests/get_config_unittest.