tuist bazel setup verifies the cache endpoint is reachable before writing .bazelrc.tuist

tuist bazel setup now probes the resolved remote cache endpoint before writing .bazelrc.tuist, regardless of whether the URL came from the server’s advertised endpoints or the TUIST_CACHE_ENDPOINT override. The probe issues the same build.bazel.remote.execution.v2.Capabilities/GetCapabilities gRPC handshake Bazel uses on start-up, validating connectivity, TLS, auth, and instance authorization. A failed probe now aborts setup with a descriptive error instead of generating config that breaks the first bazel build.