Change of support policy: one release track, on-demand releases

[tsaarni]

What do you want the project to decide?

According to current support policy, Contour should release quarterly and maintain support for three release tracks with regular patch updates https://projectcontour.io/resources/support/. However, this policy has not been followed recently due to limited resources.

I propose that we move to support a single release track at a time, with new releases made on-demand rather than following a fixed schedule.