Support native dockerconfigjson secrets when configuring docker registry for serverless

[kwiatekus]

Description
As a user I would like to configure secret of type kubernetes.io/dockerconfigjson (i.e using this tutorial) and reference it in my serverless CR to be used as external docker registry.

With Serverelss CR we allow user to declare which secret should be used.
Serverless manager should take the dockerconfigjson data and apply in the owned copy (serverless-registry-config-default) that is then being replicated accross namespaces.
For the sake of simplicity we should not force the user to fill in the extra labels or anything else than k8s standard.

Reason
Conforming with kubernetes known types of secrets simplifies the adoption of kyma serverless.
Additionally, we can reduce maintanance costs as this would allow us to rely on kubernetes CLI and deprecate the defaulting logic in our webhook that currently generates the data.dockerconfigjson content

[kyma-bot]

This issue or PR has been automatically marked as stale due to the lack of recent activity.
Thank you for your contributions.

This bot triages issues and PRs according to the following rules:

• After 60d of inactivity, lifecycle/stale is applied
• After 7d of inactivity since lifecycle/stale was applied, the issue is closed

You can:

• Mark this issue or PR as fresh with /remove-lifecycle stale
• Close this issue or PR with /close

If you think that I work incorrectly, kindly raise an issue with the problem.

/lifecycle stale

[kwiatekus]

According to POC we expect changes in

Stages: ( single release )

• support to serverless bases on dockerconfigjson (exclusively / or additionally)
• adjust serverless charts wrt. docker registry configuration
• start supporting kubernetes.io/dockerconfigjson secret type in Serverless CR
• change documentation (Configure docker registry )
• operator ( for dockerconfigjson case ) should copy user provided secret into serverless owned secret (serverless-registry-config-default)
• keep support for opaque secret: mutation webhook logic (transform opaque secret into dockerconfig ) moved to operator logic
• Migration aspects: document migration guides (both cases : OSS & SKR), depreciation notice in release notes (incl. "whats' new")

[anoipm]

https://github.com/kyma-project/kyma/blob/2.10.0/docs/03-tutorials/00-serverless/svls-07-set-external-registry.md

[pPrecel]

We figured out that the secret with type kubernetes.io/dockerconfigjson does not contain all the needed information ( like the registry address). This secret is used only to authorize the registry but we need registryAddress to know full destination path to the image destination.