chore(appconfig): add typeAsString escape hatch for custom configuration types

[dzchen22]

Issue # (if applicable)

Closes #.

Reason for this change

Allows customers to create custom configuration profile types not defined in the configuration profile enum.

Description of changes

Added a typeAsString property to the AppConfig configuration interfaces as an escape hatch that allows specifying custom configuration types as strings.

What code changes did you make?

• Added typeAsString?: string property to configuration interfaces
• Implemented effectiveType() method with precedence logic
• Updated CloudFormation resource creation to use effectiveType()

Why do these changes address the issue?

• Provides escape hatch for custom configuration types beyond predefined enum

What design decisions have you made?

• Precedence: typeAsString overrides type when both specified

Describe any new or updated permissions being added

Description of how you validated changes

Yes

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license