Describe the Jakarta Transactions 2.1 read-only feature

[scottmarlow]

Is your feature request related to a problem? Please describe.
https://github.com/jakartaee/platform/blob/main/specification/src/main/asciidoc/platform/TransactionManagement.adoc does not yet describe the Transactions 2.1 read-only feature.

Describe the solution you'd like
https://jakarta.ee/specifications/platform/11/jakarta-platform-spec-12.0#transaction-requirements should describe the Transactions 2.1 read-only feature as described in jakartaee/transactions@a60daaa#diff-a7f1a8f7aa4fe67e98dd606d2752e6380bbc1d952dbd3e46907126923ba6125e and the final Jakarta Transactions 2.1 specification.

We need to explain how read-only transactions are expected to work in Jakarta EE 12+ applications so that users know how to use this new feature correctly.

Describe alternatives you've considered
none.

Additional context

https://www.eclipse.org/lists/messaging-dev/threads.html#00135 contains a Jakarta Messaging mailing list discussion about the Transactions read-only feature.