Partner should be able to enter one's payment integration details in Admin Portal

[ElenaBelyavskaya]

As a partner, I should be able to enter my payment integration details in AdminPortal.

1. Required payment integration details are specific for particular payment provider.
   That's why AdminPortal must fetch a list of available payment providers and list of required fields for each provider.
   And as a partner, I should be able to add a payment provider from available list.
2. After payment provider is added in AdminPortal, a list of required integration properties must be displayed.
   Some properties are secrets and values for such properties can't be fetched from the backend, so only some dummy values hidden like a password can be shown for such properties.

• Non-secret properties can be fetched from the backend API and can be shown as plain text.

List of subtasks:

1. Expose endpoints for managing payment provider integration details MAVN.Service.CustomerProfile#12
2. Expose endpoint to get a list of available payment providers with their required properties MAVN.Service.PaymentManagement#3
3. openmavn/mavn.service.adminapi#15
4. openmavn/mavn.service.adminapi#29
5. openmavn/mavn.frontend.backoffice#62
6. Add optional parameters with integration details to check them before saving to DB MAVN.Service.PaymentManagement#7
7. Add optional parameter with integration details to check them before saving to DB MAVN.Service.PayrexxIntegration#2
8. OpenMAVN/MAVN.Service.AdminAPI#35

[Mamyako]

This ticket can't be fully tested since only Payrexx is available as payment provider. Required fields are static because no changes in payment provider can be made.

[ElenaBelyavskaya]

@Mamyako Vasilisa we go with just Payrexx at this stage, so this is fine.

[ElenaBelyavskaya]

Successfully tested on the demo env admin portal.