To add support for (root) username and password during cluster creation

[viggy28]

Currently, we can't create a cluster since the backend expects a username and password; however, dash doesn't support that.

[skant7]

I tried resolving the issue using the same template used for other input fields and included username and password in request body.Any suggestions be helpful. #20

[viggy28]

@skant7 is this issue good to be closed?

[viggy28]

tested and configuration page also shows the credentials. Very nice @skant7