Add support for OperationPreferences.ConcurrencyMode attribute

Hello,

I wanted to open a pull request to provide support for `OperationPreferences.ConcurrencyMode`[1] but it seems that the pinned version of aws-cdk-lib doesn't support that. Is there a plan to upgrade the package version?

```ts
export interface OperationPreferences {
readonly concurrencyMode?: ConcurrencyMode;
readonly failureToleranceCount?: number;
readonly failureTolerancePercentage?: number;
readonly maxConcurrentCount?: number;
readonly maxConcurrentPercentage?: number;
readonly regionConcurrencyType?: RegionConcurrencyType;
readonly regionOrder?: string[];
}

/**
* Specifies how the concurrency level behaves during the operation execution
*/
export enum ConcurrencyMode {
STRICT_FAILURE_TOLERANCE = 'STRICT_FAILURE_TOLERANCE',
SOFT_FAILURE_TOLERANCE = 'SOFT_FAILURE_TOLERANCE',
}

// ...

const stackSet = new cfn.CfnStackSet(this, 'Resource', {
// ...
operationPreferences: undefinedIfNoKeys({
concurrencyMode: props.operationPreferences?.concurrencyMode,
regionConcurrencyType: props.operationPreferences?.regionConcurrencyType,
maxConcurrentPercentage: props.operationPreferences?.maxConcurrentPercentage,
failureTolerancePercentage: props.operationPreferences?.failureTolerancePercentage,
}),
```

However, the generated template doesn't contain the parameter. I suspect that it's caused by the outdated `aws-cdk-lib` version.

Start by inspecting the pinned aws-cdk-lib version and the StackSet operationPreferences handling shown in the issue. Verify how the generated template is produced and whether upgrading the dependency exposes concurrencyMode; done means the generated template contains the requested parameter without regressing the existing operation preferences.

Written by the indexing model from the issue text.