made BenchPlugin more extensible to support custom CSS files #1012

Job	Run time
Test JDK 11, ubuntu-22.04	3m 4s
Test JDK 17, ubuntu-22.04	3m 1s
Test JDK 19, ubuntu-22.04	2m 55s
Deploy to github packages and Sonatype OSSRH	1m 54s
	10m 54s

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