Code uses WebClient but blocks

[marschall]

The code uses the reactive WebClient but ends up calling #block() which, as the name suggests, blocks and therefore defeats the whole purpose of using WebClient in the first place. Examples:

• CovidCertificate-App-Transformation-Service/ch-covidcertificate-backend-transformation/ch-covidcertificate-backend-transformation-ws/src/main/java/ch/admin/bag/covidcertificate/backend/transformation/ws/client/BitClientOauthImpl.java

  Line 63 in 8289bad

  .block();

• CovidCertificate-App-Transformation-Service/ch-covidcertificate-backend-transformation/ch-covidcertificate-backend-transformation-ws/src/main/java/ch/admin/bag/covidcertificate/backend/transformation/ws/client/BitClientOauthImpl.java

  Line 79 in 8289bad

  .block();

The code should instead do one of the following:

• Avoid calling #block() and instead call #subscribe()
• Switch from the reactive WebClient to the blocking RestTemplate