Allow sites to opt out of the update cooldown via a wp-config constant

[raftaar1191]

With the Protect The Shire initiative, new plugin/theme releases wait up to 24 hours before distribution through auto-updates. The upcoming "skip cooldown when Gandalf has 0 findings" iteration will shorten this for most releases, which is great.

For the remaining cases, I'd like to suggest a site-side escape hatch: a constant such as WP_SKIP_COOLDOWN_PERIOD that administrators can define in wp-config.php. When enabled, the site would receive the newest release immediately instead of the post-cooldown version.

This would help developers, agencies, and advanced users who need to deploy a critical fix right away, while keeping the cooldown as the default for everyone else. Since it requires wp-config.php access, it's an explicit opt-in — the site owner knowingly accepts the supply-chain risk for their own site.

Since the cooldown is enforced by the update API, this would need two parts: core sending a flag with its update checks, and the API honoring it. I'll open a companion Core Trac ticket for the core side and link it here.

[raftaar1191]

Companion Core ticket: ​#65678