State the 5.4 abort-marker default, restart rule and downgrade requirement in the release notes #3942

Problem

Harper 5.4 turns on storage.rocks.transactionLogAbortMarkers by default (#3928) and adds storage.rocks.transactionLogWriteIntents (default off). Operators need to know three things before upgrading:

• The new default, and false as the opt-out.
• Both settings are read once at process start, so a change needs a full restart.
• A reader without aborted-batch support treats an aborted batch as committed. That includes a 5.3 build older than the rocksdb-js 2.13.0 pin (Pin rocksdb-js 2.13.0 on v5.3 #3828) and any external tool reading the logs. So a 5.4 node's logs must not be read by such a reader: a downgrade, or restoring a backup onto an older build.

Done when

The 5.4 release notes and the configuration reference state all three. Tracked by HarperFast/documentation#780, which covers most of it.

Review-Deferral: 968b54995b7248e9 severity=nit category=documentation
Review-Deferral: 8e3b71330068c463 severity=nit category=data-integrity

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