Reducing changes in Generated SDK Sample Files for SDK PR

## Context

Today, we generate SDK samples as part of the SDK PR for release to show those samples in doc site.
However, there is a large number of generated example files included in each SDK PR.
https://github.com/Azure/azure-sdk-for-js/pull/38549

As we increasingly rely on AI in SDK PR review, the large volume of generated SDK sample files can become problematic for AI-based review.

Most of the changes were related to file mapping updates rather than meaningful sample logic changes.

## Proposal:

Introduce a `sample_metadata.json` that maps the original Swagger/TypeSpec file

For example:
```
file_shares_get_stats.py:
    x-ms-original-file: 2026-04-01/FileServicesGetUsage.json:

```

If we define this metadata format clearly, most generated sample files would no longer need to change when a new API version is introduced.
Instead, only the metadata file would be updated, which should significantly reduce PR noise and make both human and AI reviews more effective.