(gen2-migration) `generate` command should handle api overrides

### Is this feature request related to a new or existing Amplify category?

_No response_

### Is this related to another service?

_No response_

### Describe the feature you'd like to request

In Gen1, customers can override the built-in api resources by running `amplify override api`. This creates an `overrides.ts` file where customers can override resource properties using the CDK. For example

```ts
import { AmplifyApiGraphQlResourceStackTemplate, AmplifyProjectInfo } from '@aws-amplify/cli-extensibility-helper';

export function override(resources: AmplifyApiGraphQlResourceStackTemplate, amplifyProjectInfo: AmplifyProjectInfo) {
resources.api.GraphQLAPI.queryDepthLimit = 5;
}
```

Our code-generation should take this `override.ts` file into account and produce the equivalent Gen2 code.

### Describe the solution you'd like

Ideally, we would transform the `override.ts` to look like this:

```ts
export function override(backend: Backend, amplifyProjectInfo: { envName: string, projectName: string }) {
(backend.data.resources.graphqlApi.node.defaultChild as CfnGraphQLApi).queryDepthLimit = 5;
}
```

And then invoke this function from `backend.ts`:

```ts
import { override as overrideApi } from './api/override.ts`

const branchName = process.env.AWS_BRANCH ?? 'sandbox';
const backend = defineBackend({
...,
data,
});

overrideApi(backend, { envName: branchName, projectName: '' });
```

### Describe alternatives you've considered

None

### Additional context

https://github.com/aws-amplify/amplify-cli/blob/664dabc422d81153a3193996a7324d27829ef3b9/packages/amplify-cli-extensibility-helper/src/types/api/amplify-api-resource-stack-types.ts#L16-L22

Note that its also possible to override REST APIs:

https://github.com/aws-amplify/amplify-cli/blob/664dabc422d81153a3193996a7324d27829ef3b9/packages/amplify-cli-extensibility-helper/src/types/api/types.ts#L20-L26

### Is this something that you'd be interested in working on?

- [ ] 👋 I may be able to implement this feature request

### Would this feature include a breaking change?

- [ ] ⚠️ This feature might incur a breaking change

Start with the linked type definitions in amplify-cli-extensibility-helper and trace the generate command's code-generation entry point. Compare the requested api/override.ts and backend.ts flow, including both GraphQL and REST overrides; done means Gen1 override.ts files are transformed into equivalent Gen2 code and invoked from backend.ts.

Written by the indexing model from the issue text.