Prometheus health checks fail when `falcosidekick` is not enabled

[plkokanov]

What happened:
The prometheus health checks fail when falcosidekick is not enabled:

- lastTransitionTime: "2026-04-17T18:43:17Z"
  lastUpdateTime: "2026-04-17T18:45:48Z"
  message: 'There are health issues in Prometheus pod "shoot--local--local/prometheus-shoot-0".
    Access Prometheus UI and query for "healthcheck:up" for more details: healthcheck:up{job="prometheus-shoot",
    scrape_job="scrapeConfig/shoot--local--local/shoot-falco", task="scrape_pool:empty"}
    => 0'
  reason: PrometheusHealthCheckDown
  status: "False"
  type: ObservabilityComponentsHealthy

This happens because the shoot-falco scrape config is always deployed, even when falcosidekick is not enabled and there isn't anything to scrape in the shoot.

What you expected to happen:
Prometheus healthchecks to not fail.

How to reproduce it (as minimally and precisely as possible):

1. Create a Shoot cluster
2. Enable the falco extension and only specify stdout destination, e.g.:

extensions:
- providerConfig:
    apiVersion: falco.extensions.gardener.cloud/v1alpha1
    autoUpdate: true
    destinations:
    - name: stdout
    falcoVersion: 0.41.3
    kind: FalcoServiceConfig
    rules:
      standard:
      - falco-rules

3. Observe that the shoot remains unhealthy with the error shown above

Anything else we need to know:
One way to fix this would be to introduce a falcosidekick.enabled value in the extension-shoot-falco-service-chart-seed chart similar to what is done for the shoot falco chart and only include the definition for the scrape config if falcosidekick.enabled is true.

However, I wonder if it makes sense to deploy the seed extension-shoot-falco-service-seed ManagedResource when falcosidekick is not enabled as it only contains resources necessary for falcosidekick.