Remove the fallback to use generation in ComponentDescriptorCache key

[nesmabadr]

Description

Currently we use the module version from the annotation added in the ModuleTemplate as part of the ComponentDescriptorCache key. If the annotation is not found we fall back to using the generation instead. After all ModuleTemplates have the module version in them, we need to remove this fallback logic.
This is a followup item for #929

ACs:

• Remove the fallback logic to use generation as part of the componentDescriptorCache key once all ModuleTemplates have the module version assigned in the CR
  • This condition should never occur: https://github.com/kyma-project/lifecycle-manager/blob/c3e2541c8f8f5ca88f8e48019c45e2dba95f4611/internal/descriptor/cache/key.go#L18C2-L18C106
  • proper error handling implemented
• Drop the channel from the descriptor key

[janmedrek]

Version should be added as a specific field in the ModuleTemplate, until then it is blocked.

[janmedrek]

Related to versions in the Module Catalogue: #1472

[c-pius]

Do we need to block this until once all ModuleTemplates have the module version assigned in the CR is true?