[pipelines][create] Add partial support for github enterprise

[amrmahdi]

This change add partial for support for creating pipelines for github enterprise repos.

It is partial because it only supports creating pipelines with existing yaml files, requiring --yaml-path.

Partially addresses #620

Please make sure the code is following contribution guidelines in CONTRIBUTING.md

• [x] : This PR has a corresponding issue open in the Repository.
• [ ] : Approach is signed off on the issue.

[amrmahdi]

@aasiddiq Thanks for the review. Would you be able to merge the changes? And once it is merged, when you expect for this change to be officially released?

[AustinSmart]

Any chance this can be merged and released?

[coolhome]

I imagine this was not merged because it is currently not supported.

{
	"$id": "1",
	"innerException": null,
	"message": "This API does not support creating pipelines with repositories of type GitHubEnterprise.",
	"typeName": "Microsoft.Azure.Pipelines.WebApi.UnsupportedRepositoryTypeException, Microsoft.Azure.Pipelines.WebApi",
	"typeKey": "UnsupportedRepositoryTypeException",
	"errorCode": 0,
	"eventId": 3000
}

What an undocumented disappointment this has been.

UPDATE - I was able to implement the PR changes to my local install and it actually worked. The only hiccup I ran into was not knowing the service connection id (guid) instead of the name of the connection. What is preventing this from being released?