Protecting an api with a subscriptions

[r-marques]

Describe how to protect a simple api using credit based subscriptions

1. instantiate the sdk
2. login to nevermined
3. publish the web service asset
4. get details about the newly published asset

Reference: https://github.com/nevermined-io/sdk-js/blob/main/integration/external/Services_NFT1155.e2e.test.ts