POC: Skip kaniko build in serverless

[kwiatekus]

Description

Verify the following ideas:

• Serverless does not need to trigger kaniko build for Functions but instead the code and dependencies could be mounted from pv
  into serverless provided base image.
• Do not make any assumptions based on existing function controller code.
• Assume that Function CR remains backward compatible

Document the outcome as a issue comment and discuss with the team (derive recommendations for git functions).
If the ideas are validated, draw necessary diagrams explaining necessary changes in the function processing flow.

Reason
If the POC validates the idea we could eliminate the dependencies to kaniko build and docker registry. This could greatly speed up redeploying new versions of code and reduce necessary resources required to develop ideas as functions (no extra memory, cpu time or Volume storage for images).
Additionally the POC could help positioning serverless module as development tool that helps users to prove their ideas in the kyma runtimes as functions and later "eject" them into manifests that declare production-grade workloads

[kwiatekus]

Additionally @kwiatekus estimate the gain:

• how many functions are there that potentially dont need a build ?
• do customers need that immediate redeployment of changed code ?

[ptesny]

if I understand well the whole ideas is pretty much similar to the existing base function image override. ?
Power of serverless with SAP BTP, Kyma runtime. Base image override.