RELEASING.md: add the ATR (Apache Trusted Releases) path (#9264)

* RELEASING.md: add the ATR (Apache Trusted Releases) path

Document staging, voting, publishing and announcing through ATR, on the
website or from the atr command line. The SVN steps stay as the alternative.
Release managers must pick one path per release and not mix them.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

* Add the ATR vote email template and document how to use it

ATR can fetch the vote email template from a URL. The new
dev-tools/atr/start-vote-template.txt is the Storm template, built from ATR's
default with the Storm specifics from RELEASING.md (Nexus staging repository,
full and lite binaries, how to vote). It is excluded from RAT because it is sent
as an email body. RELEASING.md explains the one-time ATR setting and how the
website form and the command line use it.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

* Move the ATR vote email template to its own pull request

RELEASING.md keeps pointing at dev-tools/atr/start-vote-template.txt, which is
added by that pull request.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

* Keep the SVN email templates in RELEASING.md as they were

Restore the original dist.apache.org URLs in the SVN vote and cancel templates.
ATR users get their vote email from dev-tools/atr/start-vote-template.txt.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

* Document the ATR announcement template and the download path suffix

- One-time setup: the announce template URL and subject, and the default download
  path suffix (apache-storm-{{VERSION}}), without which ATR publishes flat into dist/release/storm/.
- Publish step: check the suffix before publishing, and how to fix it afterwards.
- Announce step: the ATR form and command line use dev-tools/atr/announce-template.txt.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

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Co-authored-by: Claude Sonnet 5.5 <noreply@anthropic.com>