As a SDP maintainer I want to have a place to record information about which lifecycle phase a specific SDP release is in.

We extended our database schema to contain information about the products within a SDP release recently.
Now we need to include lifecycle information about an SDP release itself as well.

This ticket is not about user-facing changes!

One source of inspiration for the enum variants could be this document: https://docs.google.com/document/d/1sRMS1IX0r7ZkYthDR0VY1bYyvp_6K_xw4sR1vZwla8E/edit