Add authorization mechanics for Jenkins as a Code.

Hello,

In jenkins as a code plugin, we want to load jenkins.yaml file with configuration from bitbucket repository. We encounter one problem. Authenthication in bitbucket is done through Authorization headers. Unfortunately right now jenkins as a code is not supporting adding any headers or authorization information for yamlsource as url. Solution of this problem right now can be found in this fork: https://github.com/matankatz/configuration-as-code-plugin/commit/5bc8a7fa3b55ef59c2973e82dd43730cc1df8c97

Can we add this to jenkins, because it is really very useful and needed feature if you don't want to host static yaml file.