job submission plugin accept yaml contents

In our current job cloning logic, we will pass username and jobname in the url, and the plugin will retrieve the config of specified job by REST API. This issue is discussing a new way that plugin get the content of job config (protocol yaml) directly.

The benefits of doing this:

• Other front end (python-sdk or notebook extension) could generate a basic yaml for user, and leverage the job submission page for advanced editing. This means we could add have more templates
• Clone jobs across clusters or from a job config yaml

Possible implements:

• Compress and encode the protocol yaml in url directly (be careful not to exceed 2000 char limit)
• Use a POST request with job config as body

the job submission plugin would retrieve the job config and use it