(aws-ec2): Add `InterfaceVpcEndpointAwsService.SCHEDULER` for EventBridge Scheduler

### Describe the feature

`aws-cdk-lib/aws-ec2` exposes static `InterfaceVpcEndpointAwsService` constants for most AWS services (EVENTBRIDGE, STEP_FUNCTIONS, LAMBDA, etc.), but has no constant for EventBridge Scheduler (`com.amazonaws..scheduler`).

Users must currently construct it manually:

```ts
this.vpc.addInterfaceEndpoint('SchedulerEndpoint', {
service: new InterfaceVpcEndpointAwsService('scheduler'),
});
```

### Use Case

VPC-attached Lambdas that call the EventBridge Scheduler API (aws-sdk-scheduler) need an interface VPC endpoint (or NAT egress).

Adding a supported constant would match the ergonomics of other services and avoid the surprise that Scheduler is not covered by EVENTBRIDGE (which points at events, a separate service).

### Proposed Solution

Add to packages/aws-cdk-lib/aws-ec2/lib/vpc-endpoint.ts:

```ts
public static readonly SCHEDULER = new InterfaceVpcEndpointAwsService('scheduler');
```

Region availability per AWS docs: https://docs.aws.amazon.com/scheduler/latest/UserGuide/using-vpc-endpoints.html

### Other Information

_No response_

### Acknowledgements

- [x] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### AWS CDK Library version (aws-cdk-lib)

2.258.1

### AWS CDK CLI version

2.1135.1 (build 6551740)

### Environment details (OS name and version, etc.)

Amazon Linux 2

Start with packages/aws-cdk-lib/aws-ec2/lib/vpc-endpoint.ts and review the neighboring InterfaceVpcEndpointAwsService constants. Add the Scheduler service constant described in the issue, then verify that the aws-ec2 tests pass and that the exposed constant represents the scheduler endpoint and is usable by VPC interface endpoints.

Written by the indexing model from the issue text.