Custom log filtering

[adams85]

Describe the purpose of your pull request

Provides a new, more convenient way (ConfigCatClientOptions.LogFilter) for consumers to specify custom log event filter logic.

Also, brings some performance improvements (reduced memory allocation) around log messages and evaluation log building:

ConfigCat.Client.Benchmarks.MatrixTestBenchmark

Diff	Method	Mean	Error	Allocated
Old (net6.0, LogInfo = false)	MatrixTests_ConfigV6	16.14 ms	0.149 ms	11.75 MB
New (net6.0, LogInfo = false)		16.17 ms (0%)	0.084 ms	11.53 MB (-2%)
Old (net48, LogInfo = false)	MatrixTests_ConfigV6	52.67 ms	0.157 ms	17.33 MB
New (net48, LogInfo = false)		52.53 ms (0%)	0.318 ms	16.77 MB (-3%)
Old (net6.0, LogInfo = true)	MatrixTests_ConfigV6	49.48 ms	0.204 ms	62.76 MB
New (net6.0, LogInfo = true)		48.92 ms (-1%)	0.444 ms	62.07 MB (-1%)
Old (net48, LogInfo = true)	MatrixTests_ConfigV6	138.43 ms	1.004 ms	77.65 MB
New (net48, LogInfo = true)		136.28 ms (-2%)	0.842 ms	73.94 MB (-5%)

Related issues (only if applicable)

https://trello.com/c/IxCFbq2j

Requirement checklist (only if applicable)

• [ ] I have covered the applied changes with automated tests.
• [ ] I have executed the full automated test set against my changes.
• [ ] I have validated my changes against all supported platform versions.
• [ ] I have read and accepted the contribution agreement.

[sonarcloud[bot]]

Quality Gate failed

Failed conditions
E Reliability Rating on New Code (required ≥ A)
B Maintainability Rating on New Code (required ≥ A)

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