helm_aws_profile_pattern default cannot be disabled; no opt-out when migrating to --identity

### Describe the Bug

When helm_aws_profile_pattern is not set in atmos.yaml, Atmos applies a hardcoded default value ({namespace}-{tenant}-gbl-{stage}-helm) and attempts to resolve a matching AWS config profile. There is no way to opt out of this behavior.

The deprecation warning instructs users to use --identity instead, but passing --identity does not suppress the profile pattern lookup — the default is still evaluated and the command fails if no matching AWS config profile exists.

### Expected Behavior

When a user omits helm_aws_profile_pattern and provides --identity, the deprecated profile lookup should be skipped entirely. The --identity flag should be a sufficient replacement with no additional configuration required.

### Steps to Reproduce

1. Omit helm_aws_profile_pattern from atmos.yaml (or remove it after seeing the deprecation warning)
2. Run atmos helmfile diff -s --identity
3. Observe the warning and error — Atmos resolves the default pattern {namespace}-{tenant}-gbl-{stage}-helm, fails to find the profile, and exits

### Screenshots

_No response_

### Environment

- Atmos version: 1.207.0
- OS: macOS (darwin/arm64)

### Additional Context

Workaround: explicitly set helm_aws_profile_pattern to a pattern that matches an existing AWS config profile (e.g. {stage}-{region}). The --identity flag alone is not sufficient