chore: upgrade gardener/gardener SDK to v1.154.0 - #39

## Summary of changes

### go.mod / go.sum — dependency upgrades

- `github.com/gardener/gardener` → `v1.154.0` (from pseudo-version `v1.135.2-0.20260206151026-f39065093aa7`)
- `github.com/gardener/gardener/pkg/apis` → `v1.154.0` (gardener's split-out sub-module, must match the main module version)
- `github.com/gardener/gardener-extension-provider-openstack` → `v1.58.0` (from `v1.51.0`)
- `github.com/open-telemetry/opentelemetry-operator` → `v0.162.0` (monorepo was incompatible at v0.142.0 with the new controller-runtime brought in by gardener v1.154.0)
- `golang.org/x/net` → `v0.62.0` (explicit pin; closes security PR #38, CVE-2026-78661 / CVE-2026-97045)
- `github.com/go-jose/go-jose/v4` → `v4.1.6` (explicit pin; closes security PR #37, CVE-2026-116587)
- `github.com/labstack/echo/v4` → `v4.16.1` (explicit pin; closes security PR #20, CVE-2026-55677)
- Transitive upgrades pulled in by the above, including:
  - `k8s.io/{api,apimachinery,client-go,...}` v0.34.x → v0.37.1
  - `go.opentelemetry.io/otel` v1.43.0 → v1.47.0 (closes security PRs #23–#29)
  - `google.golang.org/grpc` v1.81.0 → v1.84.0 (closes security PR #30)
  - `helm.sh/helm/v3` dropped entirely (gardener v1.154.0 migrated to helm/v4; closes security PR #31)
  - `github.com/perses/perses` v0.51.0 → v0.54.0 (closes security PR #22)
  - `github.com/open-telemetry/opentelemetry-operator/apis` v0.142.0 → v0.160.0 (closes security PR #21)
  - `github.com/google/cel-go` v0.26.1 → v0.30.0 (closes security PR #19)
  - `sigs.k8s.io/controller-runtime` v0.22.5 → v0.25.2

### .license-scan-overrides.jsonl

Added an entry for `github.com/pascaldekloe/goe` with licence type `CC0-1.0`.
This is a new transitive dependency whose LICENSE file uses non-standard Creative
Commons Zero wording that go-licence-detector cannot auto-detect, even though CC0-1.0
is already in the project allowlist.

### test/integration/webhook/shootadmission/shootadmission_test.go

Updated two expected JSON strings to reflect API changes in
`gardener-extension-provider-openstack` v1.58.0:

- The deprecated `Networks.Worker` field is now tagged `json:"worker,omitempty"`,
  so an empty string is no longer emitted during marshalling.
- Field ordering in the JSON output changed for the user-provided config round-trip
  path (`kind` now appears before `floatingPoolName`).