Docs: Clarify release process for major WP Beta 1

[gziolo]

What?

Revision to the documentation based on the discussion around WordPress 6.2 RC1 release. The changes proposed ensure that npm publishing strategy is as seamless as possible. Changes in the process successfully exercised by @Mamaduka and @ntsekouras – editor tech leads:

• wp/X-Y (wp/6.2) branch gets created from release/X-Y (release/15.1) shortly before WP Beta 1 release

[ntsekouras]

This looks good, thank you @gziolo!

[github-actions]

Flaky tests detected in 0e984e7.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/4223723383
📝 Reported issues:

• [Flaky Test] should handle Enter across blocks #39763 in specs/editor/various/multi-block-selection.test.js
• [Flaky Test] should leave a scheduled page scheduled if canceled #47499 in specs/editor/various/switch-to-draft.test.js
• [Flaky Test] should make the modal content focusable when it is scrollable #48067 in /test/e2e/specs/editor/various/a11y.spec.js
• [Flaky Test] should revert a scheduled page to a draft if confirmed #47500 in specs/editor/various/switch-to-draft.test.js

[Mamaduka]

Thank you, @gziolo 🙇