Document Watcher Certificate Setup (CM vs GCM)

[c-pius]

Description

Document the certificate setup including rotation mechanism. Depict the overall setup and what is equal between GCM and cert-manager. Show the differences between GCM and cert-manager.

Reasons

Understanding of the overall setup and its details need to be understandable.

AC

• decide whether the doc should live at lifecycle-manager or runtime-watcher
• decide whether it is an extension to https://github.com/kyma-project/runtime-watcher/blob/main/docs/architecture.md, or if this current doc should be split into two or more parts
  • e.g., one part focussing on the certificate setup, another one focusing on how to configure the watch
• use the exact terminology aligned here: [Research] have consistent watcher-related terminology lifecycle-manager#2425
• describe the overall setup including rotation applicable to both solutions
• describe where the two solutions differ (e.g. renewal of SKR certs)

[c-pius]

This needs to be revised due to the robust rotation epic.

[lindnerby]

Eventual differences:

• Lifetimes of certificates
• Rotation mechanism