add JMH benchmark CI workflow and JSON output

[bomanaps]

PR description

Fixed Issue(s)

Adds a workflow_dispatch GitHub Actions workflow that runs Besu's JMH EVM microbenchmarks against any specified branch, tag, or commit SHA and uploads results as a downloadable artifact with hardware metadata. Also enables JSON result format for JMH benchmarks in build.gradle, making results directly loadable into jmh-visualizer for performance analysis.
LF-Decentralized-Trust-Mentorships/mentorship-program#69

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