Core: adds Json value return type

[shohamazon]

Issue #, if available:

Description of changes:

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[barshaul]

have you tried using redis-rs support for the json module?
https:/amazon-contributing/redis-rs/blob/c132727bb94cb5ec8a6df14053a154645aa1d0d1/README.md?plain=1#L159
so we wont need to implement a json parser

[shachlanAmazon]

so we wont need to implement a json parser

+1. In general, you almost never want to implement a parser - someone, somewhere, wrote a library that does it better. Even if the redis-rs implementation isn't what we need, we could use some other ready-made crate.

[shohamazon]

closing this pr, with a decision to stick to the existing return type which is str.
for some languages (like Java) returning a Json object (map of lists and maps etc) is complicated.
we will add examples on how to convert the string representation of a json value to a json object in every wrapper.