aws-ecs: Metrics in imported FargateService

### Describe the bug

Currently there are 3 ways to import Fargate Service:
```
// from FargateService
fromFargateServiceArn(scope: Construct, id: string, fargateServiceArn: string): IFargateService;
fromFargateServiceAttributes(scope: Construct, id: string, attrs: FargateServiceAttributes): IBaseService;
// from BaseService
fromServiceArnWithCluster(scope: Construct, id: string, serviceArn: string): IBaseService;
```

You can see that output it is either `IBaseService` or `IFargateService`

To get metrics as they currently defined i need to get `BaseService`:
```
metric(metricName: string, props?: cloudwatch.MetricOptions): cloudwatch.Metric;
metricMemoryUtilization(props?: cloudwatch.MetricOptions): cloudwatch.Metric;
metricCpuUtilization(props?: cloudwatch.MetricOptions): cloudwatch.Metric;
```

For example `INetworkLoadBalancer` contains separate `metrics` property and i can easily use imported instance.

### Expected Behavior

Access to metrics provided via IBaseService or IFargateService

### Current Behavior

No access and no clear workaround.

### Reproduction Steps

See description please

### Possible Solution

Similar to `INetworkLoadBalancer` we can expose metrics property with defined metrics

### Additional Information/Context

_No response_

### CDK CLI Version

2.115.0 (build 58027ee)

### Framework Version

_No response_

### Node.js Version

18.x

### OS

AL2

### Language

TypeScript

### Language Version

~5.3

### Other information

_No response_

Start with the FargateService import methods and the IBaseService and IFargateService interfaces described in the issue. Compare their API with INetworkLoadBalancer's metrics property, then verify that imported Fargate services expose the listed metrics through their returned interfaces.

Written by the indexing model from the issue text.