Define Release cadence for the main projects

[cpanato]

Description

Define release cadence for :

• rekor
• cosign
• fulcio
• sigstore

with that we can publish the expected release dates for the community and also we can track the PR/Issues that we can include in the release.

[cpanato]

suggestions:

• once a month

[cpanato]

cc @lukehinds @dlorenc

[cpanato]

I will bring this topic to the community call next week (Jun/1)

[lukehinds]

sounds good to me, we could also cover how we respond to critical / security bugs