fix: remove unnecessary spec.helm.type

[leooamaral]

This pull request refactors how Helm repository URLs are handled throughout the operator, simplifying the schema and code by removing the type and namespace fields and enforcing stricter validation on URLs. The most important changes are grouped by theme below.

Schema and API simplification

• Removed the type and namespace fields from both the Helm and Extension specs in the CRD and Go API, reducing complexity and ambiguity in configuration. [1] [2] [3] [4] [5]
• Updated the CRD and Go API to validate Helm repository URLs with a minimum length and a pattern that requires either an oci:// or https:// scheme, ensuring only valid URLs are accepted. [1] [2]

Controller logic improvements

• Refactored the controller to parse and validate the Helm URL scheme directly, supporting both oci and https schemes, and providing clear error handling for unsupported schemes. [1] [2]

Documentation and sample updates

• Updated README.md and sample YAML files to use the new URL format with the oci:// prefix and removed the now-obsolete type field. [1] [2]