Separate out a more detailed release policy document

[shadowspawn]

Problem

In particular:

• mixing security policy and releases policy
• no explicit EOL date for old versions

See #2455 for detailed background.

Solution

Create a new Release Policy document with detail about release versioning, cadence, version status, and EOL dates.

ChangeLog

• add new Release Policy documentation

[shadowspawn]

I had another look at the package-support.json schema. It does allow versions with expiry dates, but I don't see a way to specify that doing security-only updates for a version.

https://github.com/nodejs/package-maintenance/blob/main/docs/PACKAGE-SUPPORT.md

The package-support.json file does not appear to have been adopted much, although it is not the only way of specifying the support info. This search gets 32 hits, two of which are for embedded versions of Commander!

https://github.com/search?q=path%3Apackage-support.json&type=code

I am tempted to delete the file! The new document covers similar material in a human readable way, so more accessible (since not widespread tooling supporting package-support.json).

[shadowspawn]

This PR proposes bumping up the support for old releases from 6 months to 12 months to give users who want to stay on a supported version more time to upgrade. The commitment means more versions to backport for a CVE.

Comparing current situation with our past policies, as of today.

Proposed, 1 year. Two old versions. Oldest Node.js is 18 for 12.x (and 13.x).

Version	First Release	Release Note	Status	End of life
14.x	2025-05-18	14.0.0	current
13.x	2024-12-30	13.0.0	maintenance	2026-05-18
12.x	2024-02-03	12.0.0	maintenance	2025-12-30

Current version and previous (#2150, #1004). One old version. Oldest Node.js is 18.

Version	First Release	Release Note	Status	End of life
14.x	2025-05-18	14.0.0	current
13.x	2024-12-30	13.0.0	maintenance	?

Six month support (#1114). Zero old versions.

Version	First Release	Release Note	Status	End of life
14.x	2025-05-18	14.0.0	current
13.x	2024-12-30	13.0.0	maintenance	2025-11-18 passed