feat: update path too long error flash bar

[JiayuW2]

Issue #, if available: Follow up for this https://github.com/aws/porting-assistant-dotnet-ui/pull/620 To add proper alerting message in UI for path too long.

Description of changes:

1. C# - CopyDirectory will return <Boolean, String> where String will be error message when exception happened
2. Add error flash bar in UI for the case FilePath + Destination Path > 260, see screen shot above

Testing done:

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