RFR: 8358: Create release notes for JMC 9.1.0

[Marcus Hirt]

Release notes and images for JMC 9.1.0.

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Commit messages:
 - 8358: 9.1.0 release notes

Changes: https://git.openjdk.org/jmc/pull/629/files
  Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=629&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-8358
  Stats: 223 lines in 25 files changed: 221 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jmc/pull/629.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/629/head:pull/629

PR: https://git.openjdk.org/jmc/pull/629