Configure available runtimes outside of function CRD

[kwiatekus]

Description

Move allowed runtimes from enum in function CRD into a configuration (i.e config map) that is consumed at validation time.

The configuration should contain:

• the list of supported runtimes
• information about deprecated runtimes
• information about default runtime

Reason Having the allowed runtimes as enum as part of v1alpha2.Function CRD is rather problematic. I.e If we want to add a runtime we need to change the CRD - which leads to a mandatory reconciliation of all functions on an upgraded runtime. - thats wasted computation resources used for nothing. Having a simple string field as spec.runtime allows more flexibility.

Related issues https://github.com/kyma-project/kyma/issues/14593

[anoipm]

I am implementing the changes described in the comment (12/08/2022), not in the original description.