Add feature option to make readline support optional

meson_options.txt:
Add feature option to allow feature based optional readline support for
the `jack_transport` executable.

Author: dvzrv

meson_options.txt

@@ -3,4 +3,5 @@ option('jack_net', type: 'feature', value: 'auto', description: 'Build the jack_
 option('jack_netsource', type: 'feature', value: 'auto', description: 'Build the jack_netsource executable (default: auto)')
 option('jack_rec', type: 'feature', value: 'auto', description: 'Build the jack_rec executable (default: auto)')
 option('opus_support', type: 'feature', value: 'auto', description: 'Build the jack_netsource executable with opus support (default: auto)')
+option('readline_support', type: 'feature', value: 'auto', description: 'Build the jack_transport executable with readline support (default: auto)')
 option('zalsa', type: 'feature', value: 'auto', description: 'Build the ZALSA internal client (default: auto)')