feat(asg): support keypair functionality for asg (#29679)

### Issue

When creating an instance directly through the asg, it is not possible to define the `keyPair`,  in addition to bringing a warning message that the `keyName` will be removed

This configuration allows sending the `keyPair` to the asg since the LaunchTemplate allows its integration

Warning:
> [WARNING] aws-cdk-lib.aws_ec2.LaunchTemplateProps#keyName is deprecated.

Closes #29237

### Reason for this change

I'm working directly with CDK and needed to implement a way to use my `keyPair` and avoid warning that `keyName` will be removed soon when i'm creating my ASG

### Description of changes

- Add `keyPair` to CommonAutoScalingGroupProps interface
- Prevent `keyPair` and `keyName` from being set at the same time
- Send `keyPair` when creating LaunchTemplate if flag `AUTOSCALING_GENERATE_LAUNCH_TEMPLATE` is enabled
- Prevent `keyPair` if the flag `AUTOSCALING_GENERATE_LAUNCH_TEMPLATE` is disabled


### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https:/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https:/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*