Update NewRelicLogForwardingHandler

[TimPansino]

Overview

• Update NewRelicLogForwardingHandler API for use without automatic instrumentation.
  • Add attribute support for context data.
  • Add logging metrics if enabled.
  • Allow formatters to be used with NewRelicLogForwardingHandler.
  • If a formatter is explicitly supplied, it's run before any processing is done is passed the unmodified log record.
  • Add dict message support.
  • As formatters are run first, formatters can use dicts or other data structures to generate a string that New Relic will ingest, without attempting to treat the record as a dict of context attributes.
  • Formatters that return a dict type instead of a string to NewRelicLogForwardingHandler will have the message contents treated as a attributes and processed, allowing flexibility.
  • With no formatter specified, dict messages are treated as attributes and processed.

Related Github Issue

Related to #731

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Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (2b14392) 81.21% compared to head (8fcc42f) 81.19%.

Files	Patch %	Lines
newrelic/api/log.py	86.66%	3 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1038 +/- ## ========================================== - Coverage 81.21% 81.19% -0.02% ========================================== Files 190 190 Lines 19728 19745 +17 Branches 3462 3468 +6 ========================================== + Hits 16022 16032 +10 - Misses 2718 2724 +6 - Partials 988 989 +1 ```

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[TimPansino]

I'm thinking while we're in this part of the code we might as well remove the old deprecated NewRelicLogHandler-what do you think?

I think we should do a round up of removing deprecated code and do just one major version bump for a whole batch.