fix(pkg/config): use provider type instead of name in unsupported type error messages

[kunal-yelgate]

Description

The error messages returned by PipedPlatformProvider.MarshalJSON() and PipedAnalysisProvider.MarshalJSON() incorrectly display the provider's Name rather than the invalid Type when an unsupported provider type is encountered.

Current Behavior

In pkg/config/piped.go, the following error messages are generated:

default:
    err = fmt.Errorf("unsupported platform provider type: %s", p.Name)

default:
    err = fmt.Errorf("unsupported analysis provider type: %s", p.Name)

As a result, users see the provider name instead of the actual invalid type value.

Example:

platformProviders:
  - name: my-provider
    type: UNKNOWN_TYPE

Current error:

unsupported platform provider type: my-provider

Expected Behavior

The error should report the unsupported type value:

unsupported platform provider type: UNKNOWN_TYPE

Benefits

• Improves debugging experience.
• Makes error messages accurate and actionable.
• Reduces confusion when diagnosing configuration issues.
• No functional behavior changes; only error message output is corrected.

[singhharsh1708]

I'd like to work on this.