DevX: auto-register the Cloud-Init provider when L2 constructs require it

[sakul-learning]

Problem

Constructs such as AutoScalingGroup can create Cloud-Init data sources internally, but an AwsStack does not register a CloudinitProvider when those resources are needed. A consumer can therefore build an otherwise complete stack and encounter this only at synthesis:

Found resources without a matching provider construct. Please make sure to add provider constructs [...] for the following providers: cloudinit

This is inconsistent with the stack-managed singleton behavior consumers see for other supporting providers, and the required manual provider registration is not obvious from the L2 API.

Discovered while validating the PR-head package from #134 in an external example project. This is not a blocker for that PR.

Reproduction

1. Create an aws.AwsStack.
2. Add a VPC and aws.compute.autoscaling.AutoScalingGroup using the normal L2 API.
3. Do not manually instantiate @cdktn/provider-cloudinit's CloudinitProvider.
4. Run app.synth().

Synthesis fails with the missing-provider validation above. Adding this manually makes the same stack synthesize successfully:

new CloudinitProvider(stack, "CloudInit");

Expected developer experience

When a TerraConstructs L2 internally introduces resources from a supporting provider, the stack should register or expose a consistent singleton for that provider, rather than requiring consumers to discover the dependency from a synthesis error.

Possible direction

Add stack-managed singleton handling for CloudinitProvider, following the existing supporting-provider patterns where appropriate, and add a synthesis test proving an ASG that needs Cloud-Init does not require manual provider setup.