new wrapper for medusa integration tests.
for now it is only applied to the modules directory, but it could be used in the api integration tests or any other integrations that requires a db and a server up and running.
It is not perfect, but I wanted to have something working and centralised before improving it, also avoiding too many conflicts with other prs
**What**
- Introduce link between Region and PaymentProvider
- Introduce API endpoint `GET /store/regions/:id/payment-providers` for retrieving providers by region
- Add tests for both
~~Opening a draft PR to discuss a couple of implementation details that we should align on~~
**What**
Add workflow and API endpoint for creating payment sessions for a payment collection. Endpoint is currently `POST /store/payment-collection/:id/payment-sessions`. I suggested an alternative in a comment below.
Please note, we intentionally do not want to support creating payment sessions in bulk, as this would become a mess when having to manage multiple calls to third-party providers.
