Feature work: log level filtering metrics

[tippmar-nr]

Adds metrics to track log lines discarded due to LogLevelDenyList configuration. Includes unit and integration tests.

I'm open to suggestions for different metric naming if folks don't like what I chose... ;-)

[codecov-commenter]

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[nrcventura]

Should the "dropped" metrics be incremented too?

[tippmar-nr]

Should the "dropped" metrics be incremented too?

I don't think so, as that metric is for tracking logs that were dropped due to capacity constraints.