--what-to-test flag silently gated to Enterprise plan with no documentation

### Build/Submit details page URL

_No response_

### Summary

The `--what-to-test` flag on `eas submit` (and `eas build --auto-submit`) is documented in the [CLI reference](https://docs.expo.dev/eas/cli/) without any mention of a plan restriction.

When used on a non-Enterprise plan, the submission fails **server-side** after already scheduling, with:

```
This submission specified the `changelog` parameter. Changelog submission is currently available for Enterprise plan only.
```

**Expected behavior:** Either the flag works for all paid plans, or the docs and CLI clearly state the Enterprise requirement — ideally with an upfront error *before* the submission is scheduled, not after it fails.

**Actual behavior:** The CLI accepts the flag without complaint, submits the job, and only then does the server reject it, wasting CI time and leaving the build unsubmitted.

The [EAS CLI reference docs](https://docs.expo.dev/eas/cli/#eas-build-submit) list `--what-to-test` with no asterisk, no plan badge, and no mention of Enterprise gating. This is a documentation and UX issue at minimum.

### Managed or bare?

Managed

### Environment

eas-cli: 13.x (managed by Expo, via GitHub Actions)
Node: 20.x
Platform: iOS submission via `eas submit`

### Error output

✖ Failed to schedule iOS submission
This submission specified the `changelog` parameter. Changelog submission is currently available for Enterprise plan only.
Request ID: d78f19e8-bd30-433f-9e32-576671b082c4
Error: GraphQL request failed.
Error: Process completed with exit code 1.

### Reproducible demo or steps to reproduce from a blank project

1. Have a non-Enterprise EAS account
2. Run `eas submit --platform ios --what-to-test "Some notes"` (or use `eas build --auto-submit --what-to-test "Some notes"`)
3. The CLI accepts the flag, schedules the submission, then the server rejects it with the Enterprise-only error

The flag is accepted client-side with no warning — the failure only happens after CI time has been spent.