[v0.30] ENGPLAT-399 Add --secure flag for TLS verification (#3781)

[loft-bot]

Backport from main to v0.30

Original PR Nr.: #3781

Backported Commits:

• 1499106 ENGPLAT-399 Add --secure flag for TLS verification (ENGPLAT-399 Add --secure flag for TLS verification #3781)

• ENGPLAT-399 respect platform insecure config

fix: respect platform insecure config instead of hardcoding InsecureSkipVerify

Thread config.Platform.Insecure through all call sites so
TLS verification is on by default and only skipped when the user
explicitly opts in via --insecure.

Closes ENGPLAT-399

• fix: preserve insecure TLS fallback during platform bootstrap

  The start command is the bootstrap flow — the platform always serves a
  self-signed certificate at this stage. Rather than reading
  config.Platform.Insecure (which defaults to false for fresh installs and
  has no --insecure flag on `vcluster platform start`), bootstrap probes
  and login should handle self-signed certs directly:

  • Readiness probes (port-forward, router, reachability) always skip TLS
    verification since they are unauthenticated health checks against a
    just-installed instance
  • Login tries secure first, falls back to insecure on TLS error, and
    persists the decision to config for future CLI operations

  The Transport(insecure), IsLoftReachable(insecure), and clihelper/http
  test additions from the original PR are preserved — post-bootstrap
  commands (login, connect) still respect config.Platform.Insecure.

• Revert " fix: preserve insecure TLS fallback during platform bootstrap"

This reverts commit d5181a1.

• feat: add --insecure flag to vcluster platform start

  Allows users to skip TLS certificate verification during bootstrap when
  the platform serves a self-signed certificate. The flag sets
  config.Platform.Insecure in memory so all downstream health checks and
  login calls respect it, and LoginWithAccessKey persists the value for
  future CLI operations.

• Switch flag from insecure to secure

Defaults to current insecure behavior to preserve current bootstrapping
functionality.

[loft-bot]

Unresolved Merge Conflicts Detected

This PR contains unresolved merge conflict markers. Please resolve them before merging.

Conflicted Files

./cmd/vclusterctl/cmd/platform/start.go:90:<<<<<<< HEAD
./pkg/cli/start/login.go:73:<<<<<<< HEAD

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