[FEATURE]: add Valkey CRD for standalone instances

[deepakpunjabi]

Pre-flight checks

• I have searched existing issues and discussions and could not find a duplicate.

Problem / Use case

Add Valkey CRD for standalone instances. This is fundamental block for upcoming ValkeySentinel and ValkeyCell CRDs.

Proposed solution

Add type Valkey CRD.

Scope of change

Large (new CRD, major behaviour change, requires design doc)

API / behaviour impact

• This change is backwards-compatible with existing ValkeyCluster CRs.
• This change introduces a breaking API change in v1alpha1.

Contribution

• I would like to implement this feature myself.
• I would like to help review or test this feature.

Additional context

No response