API/UI: Support custom-constrained and custom-unconstrained offerings when creating a CKS cluster

### problem

Currently, users are unable to select the custom-constrained and custom-unconstrained offerings from the UI

And also it's not even possible from the API as we are excluding the custom offerings for cks cluster

```
localcloud) 🐱 > create kubernetescluster name=test zoneid=fb0bd189-c018-4897-8a2d-7f9b59b204da hypervisor=KVM kubernetesversionid=515fb765-38f3-4ca1-bd6d-18816b64418b serviceofferingid=7ebfd3b9-1b0e-44ca-b9ec-4ebeff9df06e size=1

🙈 Error: (HTTP 530, error code 9999) Given service offering ID: Service offering {"id":13,"name":"Large Instance-unconstrained","uuid":"7ebfd3b9-1b0e-44ca-b9ec-4ebeff9df06e"}. for WORKER nodes is not suitable for the Kubernetes cluster version KubernetesSupportedVersion {"id":1,"name":"cks-csi","semanticVersion":"1.33.1","uuid":"515fb765-38f3-4ca1-bd6d-18816b64418b"} - Custom service offerings are not supported for creating clusters, service offering ID: 7ebfd3b9-1b0e-44ca-b9ec-4ebeff9df06e

(localcloud) 🐱 > create kubernetescluster name=test zoneid=fb0bd189-c018-4897-8a2d-7f9b59b204da hypervisor=KVM kubernetesversionid=515fb765-38f3-4ca1-bd6d-18816b64418b
serviceofferingid=bdf374a9-c55b-46dc-b5c1-c8056beb8d10 size=1

🙈 Error: (HTTP 530, error code 9999) Given service offering ID: Service offering {"id":14,"name":"Large-Instance-constrained","uuid":"bdf374a9-c55b-46dc-b5c1-c8056beb8d10"}. for WORKER nodes is not suitable for the Kubernetes cluster version KubernetesSupportedVersion {"id":1,"name":"cks-csi","semanticVersion":"1.33.1","uuid":"515fb765-38f3-4ca1-bd6d-18816b64418b"} - Custom service offerings are not supported for creating clusters, service offering ID: bdf374a9-c55b-46dc-b5c1-c8056beb8d10

```

### versions

ACS 4.21, 4.20.1

### The steps to reproduce the bug

1. Navigate to service offering > compute offering > create a custom-constrained and custom-unconstrained offering.

Create a custom -constrained offering od 2 cpu and 2048 ram which is the minimum requirement for a cks cluster

2. Navigate to compute > kubernetes > create cks cluster

3. The custom-constrained and custom-unconstrained are listed

...

### What to do about it?

User should be able to select the custom-constrained and custom-unconstrained offerings for a cks cluster.

As it would be beneficial for the end user to specify the CPU and memory during CKS creation

A similar box related to deploy instance should be displayed during cks creation

Beginne damit, die Erstellung von CKS-Clustern durch API und UI nachzuverfolgen, und konzentriere dich darauf, an welcher Stelle custom-constrained und custom-unconstrained Service-Angebote ausgeschlossen werden. Reproduziere das Problem mit den im Bericht beschriebenen benutzerdefinierten Angeboten. Die Aufgabe ist abgeschlossen, wenn beide Angebote im CKS-Erstellungsprozess ausgewählt und von der API akzeptiert werden.

Vom Indexierungsmodell aus dem Issue-Text verfasst.