Add simple support page

[jtnord]

Describe your use-case which is not covered by existing documentation.

if you search for support on jenkins.io you don't get any meaningful results.

Previously on the wiki we had a commercial support page, but progress on replacing that stagnated in 2022.

There should be a simple page that explains how a user can get support and what expectations they should have

Reference any relevant documentation, other materials or issues/pull requests that can be used for inspiration.

https://wiki.jenkins.io/display/JENKINS/Commercial+Support
https://community.jenkins.io/t/idea-commercial-support-vendors/2924

Are you interested in contributing a fix?

#8357