[Doc] Pulsar release policy and matrix

[tisonkun]

Search before asking

• I searched in the issues and found nothing similar.

What issue do you find in Pulsar docs?

Since #15966 accepted, we should update the website to document the release policy and releases matrix.

Currently, we have a release note page, which can be extended to serve this requirement.

What is your suggestion?

Part 1 - Prepare a release matrix like https://endoflife.date/python in https://pulsar.apache.org/release-notes/.

Part 2 - Improve the version policy page in https://pulsar.apache.org/contribute/version-policy/.

Any reference?

• https://github.com/apache/pulsar/wiki/PIP-47%3A-Time-Based-Release-Plan

Are you willing to submit a PR?

• I'm willing to submit a PR!

[tisonkun]

After another look I'd prefer to keep the release note page as is - only set a link to the release policy page. And place the matrix in the release policy page.

We may duplicate a bit the info somewhere as we can generate the matrix as a reusable react component.