refactor(ecs-patterns): organize hierarchy of describe in tests (#29153)

### Issue # (if applicable)

part of #29041, #29039

Closes #<issue number here>.

### Reason for this change


The testing hierarchy was disorganized.

### Description of changes

Organized test as below.
No logical change.

```ts
describe('Application Load Balancer', () => {

  describe('ApplicationLoadBalancedFargateService', () => {
  ...
  })

  describe('ApplicationMultipleTargetGroupsFargateService', () => {
  ...
  })
})

describe('Network Load Balancer', () => {
  describe('NetworkLoadBalancedFargateService', () => {
  ...
  })

  describe('NetworkMultipleTargetGroupsFargateService', () => {
  ...
  })
})
```





### Description of how you validated changes


pass unit tests

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

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