fix: C# template build failure after copied to a new bot folder

[luhan2017]

Description

Disable StyleCop Rule : SA1412: StoreFilesAsUtf8BOM

This rule needs all files be UTF8BOM format. But when we copy bot template to new created bot folder, it will be saved as UTF8 defaultly. This pr is to disable this rule to fix that issue.

Task Item

fixes #1577

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

Please include screenshots or gifs if your PR include UX changes.