AzureDevOpsDsc: Change PAT type to `PSCredential`

[SphenicPaul]

Logging this issue off the back of the initial PR (#7) so it's logged and not missed...

Details of the scenario you tried and the problem that is occurring

String data type isn't a suitable/ideal type to hold/pass Personal Access Tokens.

Suggested solution to the issue

Update $Pat variables/parameters to use a PSCredential type, although unclear of most suitable option at present:

• i) Have every Resource take a $Pat and $ApiUri parameter (where $Pat is updated to be a PSCredential type)
• ii) Define a new Connection class which holds ApiUri and PAT information, and which is passed between functions
• iii) Use the existing Connection class (as part of current, Azure DevOps, client libraries) ... less preferred perhaps as it couples this module with that?

[johlju]

If PAT is a key that should not be shared then it should be a PSCredential so it is encrypted in the compiled configuration. Otherwise it will be visible in the compiled configuration making it a security problem.