Remove deprecated proxy fields from Provider API

[cappyzawa]

Remove deprecated proxy fields from Provider API

Background

The deprecated proxy configuration fields need to be removed as planned. These fields were marked for deprecation in PR #1133 when spec.proxySecretRef was introduced as the recommended approach.

Deprecated Fields to Remove

1. spec.proxy field

• Location: Provider spec
• Deprecated since: v2.7 (#1133)
• Replacement: spec.proxySecretRef
• Current warning: "spec.proxy is deprecated, please use spec.proxySecretRef instead. Support for this field will be removed in v1."

2. proxy key in secret

• Location: Referenced secret data
• Deprecated since: v2.7 (#1133)
• Replacement: spec.proxySecretRef with address key
• Current warning: "specifying proxy with 'proxy' key in the referenced secret is deprecated, use spec.proxySecretRef with 'address' key instead. Support for the 'proxy' key will be removed in v1."

Timeline

• Target: After Flux v2.7 release (around September 2025)
• Rationale: Need one release cycle with deprecation warnings before removal

Implementation Tasks

• [ ] Remove deprecated proxy fields from API and controller logic
• [ ] Optimize URL parsing to eliminate redundant parsing across notifiers
  • https://github.com/fluxcd/notification-controller/pull/1133#pullrequestreview-2966720020
• [ ] Update documentation and examples