Add shell macro support

[ponchofiesta]

Please describe your feature request.
yq should support sh macros to allow any custom string manipulation.

Describe the solution you'd like

Example:

There is a secrets file like this:

a:
  token: "abcdef"
b:
  token: "xyz"

I want to get some hashes of these secrets:

yq -o=tsv '.. | { "k": path | join("."), "v": .token | @sh "echo -n ${1} | sha256sum | cut -d\' \' -f1" } | .k + ": " + .v' secrets.yml

This should print something like:

a: ae0666f161fed1a5dde998bbd0e140550d2da0db27db1d0e31e370f2bd366a57
b: f34fe622a8fe7565fc15be3ce8bc43d7e32a0dd744ebef509fa0bdb130c0ac31

Describe alternatives you've considered
Using shell with multiple lines of code

Additional context

[ponchofiesta]

Similar by the chosen example but not exactly the same: #2283