Unify MultipathStrategy and PortDirection

[fujiapple852]

Trippy currently supports a subset of the combinations of protocol, src and dest ports, and ecmp modes. These are set using the following parameters:

  -p, --protocol <PROTOCOL>                      Tracing protocol [default: icmp] [possible values: icmp, udp, tcp]
  -P, --target-port <TARGET_PORT>                The target port (TCP & UDP only) [default: 80]
  -S, --source-port <SOURCE_PORT>                The source port (TCP & UDP only) [default: auto]
  -R, --multipath-strategy <MULTIPATH_STRATEGY>  The Equal-cost Multi-Path routing strategy (IPv4/UDP only) [default: classic] [possible values: classic, paris, dublin]

These are modelled using the TracerProtocol, PortDirection and MultipathStrategy types.

The goal is to unify these types and provide a simpler set of parameters.

For IPv4/UDP the supported combinations are:

Protocol	Strategy	Source Port	Target Port	Supported
UDP	Classic	Fixed	Variable	✅
UDP	Classic	Variable	Fixed	✅
UDP	Classic	Fixed	Fixed	❌
UDP	Classic	Variable	Variable	❌
UDP	Dublin	Fixed	Variable	✅
UDP	Dublin	Variable	Fixed	✅
UDP	Dublin	Fixed	Fixed	✅
UDP	Dublin	Variable	Variable	❌