Add --icmp command line shortcut

[fujiapple852]

Users may specify --udp and --tcp as shortcuts to --protocol udp (-p udp) and --protocol tcp (-p tcp) respectively.

For example for udp:

/// Trace using the UDP protocol
#[arg(
    long,
    display_order = 3,
    conflicts_with = "protocol",
    conflicts_with = "tcp"
)]
pub udp: bool,

If neither is specified then the icmp protocol is chosen by default:

/// The default value for `protocol`.
pub const DEFAULT_STRATEGY_PROTOCOL: Protocol = Protocol::Icmp;

let protocol = cfg_layer(
    args.protocol,
    cfg_file_strategy.protocol,
    constants::DEFAULT_STRATEGY_PROTOCOL,
);

However the protocol may also be specified in the config file:

#
# Tracing strategy configuration.
#
[strategy]

# The tracing protocol.
#
# Allowed values are:
#   icmp [default]
#   udp
#   tcp
protocol = "icmp"

The user may wish to override the value from the config file with another protocol specified via the command line. To do so for icmp the user must use the longer --protocol icmp (-p icmp) form as there is no --icmp shortcut. Therefore it would be useful to add a --icmp command line shortcut.

[trkelly23]

I will be testing the changes and might need a few questions answered. Where should I post them, here?

[fujiapple852]

@trkelly23 here is fine or you can find me on discord or matrix (same username)