Allow to use yaml instead of json

[anti-social]

Yaml is more convenient for writing and modifying big chunks of data. So my suggest is to add yaml support.

It is possible to do in 2 ways:

• add an option like -data-yaml (possibly with a short version -Y) for using instead of -d
• autodetect yaml if there is a --- mark in the first line of data

[jhump]

As a work-around, you can use the tool yq and pipe your input through that and into the stdin of grpcurl. IIRC, yq . will print the input as JSON.