[dotnet client] Add CI for building, testing, license checking and codeQL check

[Han G]

Hi folks,

I’ve created a PR to add CI for building, testing, license checking and codeQL 
check for ShenYu dotnet client. Please help to review and let me know if any 
comment. Thanks for your time!

PR: https://github.com/apache/incubator-shenyu-client-dotnet/pull/15.
ISSUE: https://github.com/apache/incubator-shenyu-client-dotnet/issues/14

Thanks,
Han