RFR: CODETOOLS-7903231: Add changelog to jtreg

[Jonathan Gibbons]

CODETOOLS-7903231: Add changelog to jtreg

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Commit messages:
 - more formatting updates
 - remove SHA hashes, improve formatting
 - CODETOOLS-7903231: Add changelog to jtreg

Changes: https://git.openjdk.org/jtreg/pull/133/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=133&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903231
  Stats: 174 lines in 1 file changed: 174 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jtreg/pull/133.diff
  Fetch: git fetch https://git.openjdk.org/jtreg pull/133/head:pull/133

PR: https://git.openjdk.org/jtreg/pull/133