[backport rh-test] make 'require subscription' toggleable (#6147)

## Summary

Backport of PR #6144 to the `rh-test` branch.

This adds build time feature flags system starting with a flag that
indicates whether subscription is required to use the app. This is only
used on cloud.

## Changes

- Added build feature flags system via `__BUILD_FLAGS__` global
- Added `REQUIRE_SUBSCRIPTION` flag that can be set via environment
variable
- Conditionally load subscription-related components based on the flag
- Updated run button logic to respect the subscription requirement flag
- Updated settings UI to show subscription panel only when required

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6147-Backport-make-require-subscription-toggleable-in-build-to-rh-test-2916d73d365081e89bcfc4502315a812)
by [Unito](https://www.unito.io)

src/platform/cloud/subscription/composables/useSubscription.ts

@@ -26,7 +26,7 @@ interface CloudSubscriptionStatusResponse {
 const subscriptionStatus = ref<CloudSubscriptionStatusResponse | null>(null)
 
 const isActiveSubscription = computed(() => {
-  if (!isCloud) return true
+  if (!isCloud || !__BUILD_FLAGS__.REQUIRE_SUBSCRIPTION) return true
 
   return subscriptionStatus.value?.is_active ?? false
 })