Fixes #17284

Description

This PR adds a new function JSON_MERGE_AGGR(,<JSON 1>, <JSON 2> .... ) which performs the aggregation when the leaf elements have the same key.

Currently only two aggregators are added - ADD & MULTIPLY
For Array, it retains the functionality of JSON_MERGE function.

Example

JSON_MERGE_AGGR('ADD', {"key": 2}, {"key":3}) -> {"key":5}
JSON_MERGE_AGGR('MULTIPLY', {"key": {"k2": 2}}, {"key":{"k2":3}}) -> {"key":{"k2":6}}

Retained JSON_MERGE functionality

JSON_MERGE_AGGR('ADD', {"key": [1,2,3]}, {"key":[4,5]}) -> {"key":[1,2,3,4,5]}
JSON_MERGE_AGGR('ADD', {"key": [1,2]}, {"key":3}) -> {"key":3}
JSON_MERGE_AGGR('ADD', [1,2,3], [4,5]) -> [1,2,3,4,5]

Key changed/added classes in this PR

• json_merge_aggr expression function
• json_merge_aggr sql function

This PR has:

• been self-reviewed.
  • using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• added documentation for new or modified features or behaviors.
• a release note entry in the PR description.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• added or updated version, license, or notice information in licenses.yaml
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• added integration tests.
• been tested in a test Druid cluster.