made BenchPlugin more extensible to support custom CSS files #1015

Job	Run time
Test JDK 11, ubuntu-22.04	3m 6s
Test JDK 17, ubuntu-22.04	2m 56s
Test JDK 19, ubuntu-22.04	3m 2s
Deploy to github packages and Sonatype OSSRH	2m 9s
	11m 13s

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