Support bitbucket access token authorization

[isinghdm]

Summary / Background

Right now, CML only supports basic auth based on usernames and passwords which have a very wider access scope and are not recommended security wise if we want to just post comments using cml. It would be good to use bitbucket access token that can be generated on the fly using bitbucket API and use it in the CML pipelines.

Scope

Allow the use of bitbucket access tokens while using cml commands. Right now it returns unauthorised.