Handle IPv6 endpoints in URL parser

[officialasishkumar]

Description

Bug fix for endpoint parsing in pkg/url.ParseEndpoint.

The parser previously split url.Host on every :, which rejected valid bracketed IPv6 URL endpoints such as https://[fd00::1]:443. This updates the parser to use the standard library host/port parser so DNS names, IPv4 hosts, and bracketed IPv6 hosts are handled consistently while malformed endpoints still fail validation.

Fixes #4749

Validation run:

• go test ./pkg/url
• go test ./pkg/controller/logcollector ./pkg/controller/nonclusterhost ./pkg/controller/manager
• go test ./pkg/render

go test ./pkg/render/... was also attempted, but pkg/render/istio requires base.tgz, which is not present in a fresh clone.

Release Note

Parse endpoint validation now accepts bracketed IPv6 URL endpoints.

For PR author

• Tests for change.
• If changing pkg/apis/, run make gen-files
• If changing versions, run make gen-versions

For PR reviewers

A note for code reviewers - all pull requests must have the following:

• Milestone set according to targeted release.
• Appropriate labels:
  • kind/bug if this is a bugfix.
  • kind/enhancement if this is a a new feature.
  • enterprise if this PR applies to Calico Enterprise only.