Allow use of POST requests for long stories

Problem/Motivation

When trying to represent a story with a large amount of argument data, such as https://designsystem.digital.gov/components/table/#sticky-table-headers-2, the GET request produced by the stories.json file can be too long, causing a 419 server error when the request hits the server.

Steps to reproduce

1. Generate a story with substantial arguments.
2. Try to load the story in storybook
3. Get fatal server error

Proposed resolution

The CL_Server precursor module allowed GET or POST requests.

We would propose restoring that feature and providing a means for switching mode, ideally on a per-story basis, but that is not required.

Remaining tasks

1. Refactor to allow POST requests
2. Allow changing between GET and POST as desired

User interface changes

None

API changes

POST becomes allowed.

Data model changes

None?