fix(video): Make sure create session returned JSON, and fixed return type

[dragonmantank]

Description

• Corrected a bug introduced where Form Submission requests weren't setting the accept header, this now sets it to application/json
• Corrected an issue where the return value of the video Create Session call was accidentally changed from an array to an object

Motivation and Context

These were two bugs that were stopping calls to video's Create Session endpoint from returning properly. The calls succeeded, we just didn't report back the correct info to the developer.

Testing Details

Manual and unit tests

Example Output or Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.