RFR: JMH Pre-Integration Tests workflow

[Aleksey Shipilev]

This adds the basic pre-integration test workflow for the project.

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Commit messages:
 - Disable commit on push
 - Merge branch 'master' into gh-actions
 - Merge branch 'master' into gh-actions
 - Merge branch 'master' into gh-actions
 - Drop max-parallel from pre-integration workflow
 - Testing more extensive configuration space
 - Mention pre-integration workflow in README
 - Basic pre-integration workflow for JMH

Changes: https://git.openjdk.java.net/jmh/pull/5/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmh&pr=5&range=00
  Stats: 37 lines in 2 files changed: 37 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jmh/pull/5.diff
  Fetch: git fetch https://git.openjdk.java.net/jmh pull/5/head:pull/5

PR: https://git.openjdk.java.net/jmh/pull/5