RFC: Release cadence, process and ideas

[gouthamve]

We've decided to do a cortex release soon, but after the first release, I think we should have some process and cadence for future releases. I made a Google docs with initial suggestions here: https://docs.google.com/document/d/1Ma5upv_lPG0KaJySqm8AY20ZjicNrB2qZS5WIlDqbNw/edit#

This is largely inspired by the Prometheus release cadence and process.

[avicshw]

@gouthamve Is there any progress?

[gouthamve]

Closing as this is done in #1470