fix: QnA Maker EndpointKey is null Issue

[VanyLaw]

Description

This PR is to fix this Issue
Ref

Root Cause
This Issue is because the botproject(runtime) read qna.endpointkey from disk before, and we omit it as a fixed sensitive property. But It's more like a self-defined property and no need to omit.

Task Item

closes #1538

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code refactor (non-breaking change which improve code quality, clean up, add tests, etc)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Doc update (document update)

Checklist

• I have added tests that prove my fix is effective or that my feature works
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have functionally tested my change

Screenshots

During the QnaMaker trace, it won't show "Object not set to instance of an object" anymore.