fix: Fail early for storage size mismatch in EC2

[kichik]

Throw an exception during build time if the EC2 runner storage size is smaller than the AMI size set in the image builder. Before this change, code like this:

new GitHubRunners(stack, 'runners', {
  providers: [
    new Ec2RunnerProvider(stack, 'EC2 Linux', {
      imageBuilder: Ec2RunnerProvider.imageBuilder(stack, 'EC2 Linux Builder', {
        awsImageBuilderOptions: {
          storageSize: cdk.Size.gibibytes(100),
        },
      }),
      storageSize: cdk.Size.gibibytes(30),
    }),
  ],
});

could result in errors in the step function that are harder to debug:

Ec2.Ec2Exception: Volume of size 30GB is smaller than snapshot 'snap-0123456789abc', expect size>= 100GB