External Gateway CRD status implementation

[strekm]

Description

Extend External Gateway implementation to add meaningful status containing description and conditions. CR reconciliation should watch sub-resource lifecycle and report back to CR status. If sub-resource got status implemented it should be used to calculate CR status. If sub-resource operation, such as create, update, delete, fails it should be reflected on CR status. Finally if in code validation of CR fails it also should be reflected on a status.

Reasons
Provide easy way to troubleshoot External Gateway configuration

ACs:

• CR status properly calculated based on sub-resources and in code validation

TODOs:

• extend existing ADR
• status implementation (including conditions)
• integration test implementation based on in memory controller

Attachments
example impl: https://github.com/kyma-project/serverless/tree/main/components/operator/internal/stateex