(region-info): add GuardDuty agent repository info

### Describe the feature

I propose adding constants for the GuardDuty Runtime Monitoring agent ECR repository URIs to the region-info module.

The [AWS documentation](https://docs.aws.amazon.com/guardduty/latest/ug/runtime-monitoring-ecr-repository-gdu-agent.html) provides a list of ECR repositories for GuardDuty Runtime Monitoring agents per region. Making these URIs available as constants in CDK will allow users to programmatically reference the correct repository for each region.

### Use Case

Currently, CDK users who want to automate GuardDuty Runtime Monitoring agent deployments need to manually look up the ECR repository URI for each region. This process is error-prone and inconvenient, especially for multi-region solutions.

Providing this information in `region-info` will:

- Save users from having to maintain their own mapping of region to repository URI.
- Make it easier to implement L2 constructs (such as granting permissions to Task Execution Roles) that interact with the GuardDuty agent repository.
- Increase consistency with other managed service agent repositories already available in `region-info`.

### Proposed Solution

Implementation would follow a similar approach as pr #25928

- Add mappings of constants for the GuardDuty agent ECR repository URIs.
- Extend the generation logic accordingly.
- Provide a method for reference (implementing as an info Fact/RegionInfo).

### Other Information

Reference: [GuardDuty documentation — Runtime Monitoring ECR repositories](https://docs.aws.amazon.com/guardduty/latest/ug/runtime-monitoring-ecr-repository-gdu-agent.html)

Scope: Only the constant definitions in region-info are included here.
L2 enhancements are intentionally left for future or separate issues.

For `ECR repository for EKS agent versions 1.10.0 - 1.8.1 (eks.build.2)`, each region has either one or two repository URIs. Currently, there is no precedent in `region-info` for constant definitions that can have multiple values per region. I do not yet have a good idea for how to represent this pattern.

### 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)

2.206.0

### AWS CDK CLI version

2.1021.0

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

MacOS 14.5

Start with the region-info module and its generation logic, then compare the approach used in PR #25928. Check the AWS GuardDuty documentation for the per-region ECR repository URIs, including regions with two values, and determine how existing Facts or RegionInfo methods represent them. Done means the generated constants and reference method expose the documented repositories without adding L2 enhancements.

Written by the indexing model from the issue text.