chore(appconfig): compilation error in ts 4.2 and below because of using get in interface

[xazhao]

Reason for this change

There is a lint error which get syntax can't be used on interface before TS version 4.3

Description of changes

Replace get with a regular function.

Description of how you validated changes

Unit test passed.

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

[aws-cdk-automation]

The pull request linter has failed. See the aws-cdk-automation comment below for failure reasons. If you believe this pull request should receive an exemption, please comment and provide a justification.

A comment requesting an exemption should contain the text Exemption Request. Additionally, if clarification is needed add Clarification Request to a comment.

[xazhao]

Exemption Request: fix the lint error. The current unit tests and integration test will cover this change.

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: e00d073
• Result: SUCCEEDED
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✅ Updated pull request passes all PRLinter validations. Dismissing previous PRLinter review.

[mergify]

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