Add BIG_SUM SQL function

[rash67]

Description

This adds a sql function, "BIG_SUM", that uses CompressedBigDecimal to do a sum. Other misc changes:

1. handle NumberFormatExceptions when parsing a string (default to set
   to 0, configurable in agg factory to be strict and throw on error)
2. format pom file (whitespace) + add dependency
3. scaleUp -> scale and always require scale as a parameter

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Key changed/added classes in this PR

• CompressedBigDecimalSqlAggregator - sql function definitions and arg parsing

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This PR has:

• been self-reviewed.
• added documentation for new or modified features or behaviors.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• 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.

[rash67]

ugh, this should be stacked on #13086
ignore first commit

[2bethere]

I realized this one has no docs attached. Can you help describe what is now possible that weren't possible before with BIG_SUM so that we can include this in the release notes? cc' @317brian