Implement WindowsCredentialsDatabaseSelector

[shreyamalviya]

What does this PR do?

Adds the WindowsCredentialsDatabaseSelector component for #3426

PR Checklist

• Have you added an explanation of what your changes do and why you'd like to include them?
• Is the TravisCI build passing?
• Was the CHANGELOG.md updated to reflect the changes?
• Was the documentation framework updated to reflect the changes?
• Have you checked that you haven't introduced any duplicate code?

Testing Checklist

• Added relevant unit tests?
• Do all unit tests pass?
• Do all end-to-end tests pass?
• Any other testing performed?

  Tested by running the selector and verifying the result

• If applicable, add screenshots or log transcripts of the feature working

[mssalvatore]

Missing unit tests.

[mssalvatore]

I think all the PurePaths need to just be Paths.

Pure paths are useful in some special cases; for example:

• If you want to manipulate Windows paths on a Unix machine (or vice versa). You cannot instantiate a WindowsPath when running on Unix, but you can instantiate PureWindowsPath.

• You want to make sure that your code only manipulates paths without actually accessing the OS. In this case, instantiating one of the pure classes may be useful since those simply don’t have any OS-accessing operations.

https://docs.python.org/3/library/pathlib.html