Substitute mode for json-iter

[amarao]

Found need for 'substitute' mode - add/replace element of object (inside array) based on output of program with specified args.

Example:
[
{ "uuid": , "data": },
...
]

cat example.json|json-iter --substitute --key-name='owner' get-owner {.uuid}

result:

[
{ "uuid": , "owner": , "data": },
...
]