Service modularization todos

[ChristiaanScheermeijer]

I've collected some TODOs from the service modularization PR #363 so we don't forget.

@AntonLantukh @dbudzins Feel free to add or remove items from the lists.

TODOs:

• Move integration service files into folders e.g., ./src/services/integrations/jwp/InPlayerAccountService.ts
• Refactor entitlement service(s) to align with the integration better
• Refactor isSandbox from all service calls (not sure about this yet)
• Obtain the access model via integration (by optionally passing the media item?)

Minor TODOs (long term):

• Make integration interfaces more generic for different implementations (currently following Cleeng schemas and APIs)
• Dynamically load and bind integration files in IoC based on directory structure

[ChristiaanScheermeijer]

Some TODOs are solved in #450