feat(producer): refactor encapsulation and configuration

[lspgn]

For protobuf producer (converting from sFlow/NetFlow/IPFIX into a unique protobuf sample). This includes work from #306 #236 in regards to encapsulation:

• refactoring of the configuration with interfaces (eg: for library use)
• the packet parser implementation has an environment to allow custom layer parser and port parsding
• improve parsing function (GetBytes)
• refactoring of the packet parsing (sFlow and IPFIX datagrams)
  • not a loop anymore
• encapsulated fields are parsed separately
• add Geneve, GRE IPv6 Routing Header (srv6) parsing

TODO:

• cleanup old legacy code
• proof read docs
• make sure a mapping can be truncated (eg: dump up to 1500 bytes above ipv6 layer...)