feat(api): add support for multiple worker threads

[jordanshatford]

Describe the problem

Right now the API on works when running with a single worker thread. This could cause slowdowns when there are many requests at once.

NOTE: When content is actually downloaded, a task is added to a thread pool to perform those actions. This thread pool is configured as None which will use the number of logical CPU's available. This means that only API requests could cause a bottleneck.

Describe the proposed solution

Update the API codebase to support multiple worker threads. This could be done by using some sort of shared memory, Redis cache, or database. Implementation does not really matter, assuming that it works and is not causing another bottleneck that is worse than current functionality.

Alternatives considered

N/A

Importance

nice to have

Additional information

This will require that the current session manager class is available for all worker thread. This is to ensure that one users session information is available if many worker threads are process different requests by that user. Without this we could see duplicate content requests, failed requests, etc.