Add json_merge script function

[vladpaiu]

Summary
Add json_merge script function

Details
When using provisioning things via JSON on a multi-layered approach it sometimes useful to merge the 'child' layer with the 'parent' layer for inheriting attributes that are not overwritten and for overwriting attributes that specifically come form the child ( patch ) layer.

Solution
Add json_merge script function

Compatibility
Backwards compatible

[bogdan-iancu]

@vladpaiu , thanks for the contribution here - could you check the failed test from the CI system and get them fixed please?

[vladpaiu]

all of the CI/CD failures are not related to this PR changes:

cachedb/cachedb_dict.c:481:31: error: format specifies type 'long' but the argument has type 'int64_t' (aka 'long long') [-Werror,-Wformat]
481 | i += sprintf(obj+i, "%ld", pair->val.val.i64);