fix: Use context-aware HTTP request in DAS Rest client HealthCheck

[vtjl10]

• Summary: Replace http.Get with a context-aware request (http.NewRequestWithContext + http.DefaultClient.Do) in daprovider/das/restful_client.go to honor cancellation and timeouts.
• Behavior: HealthCheck now respects the provided Context; cancellation/deadline cleanly aborts the request. Response handling remains unchanged.
• Rationale: Prevents potential hangs during shutdown or transient network issues; improves robustness and resource management.