`ims` Service `getAccessToken` Should hide exceptions

### Expected Behaviour

When an exception occurs in the fetching of a new Access token, the IMS Service should capture any possible Feign runtime exceptions and either:

a) log it, returning nothing.
b) Transform it the exception into a meaningful, recoverable or non-recoverable state.

### Actual Behaviour

All of the Feign runtime exceptions bubble up to the caller.

Start at the IMS Service getAccessToken flow described in the issue and inspect how Feign runtime exceptions reach its caller. Confirm the intended handling with the issue's two proposed outcomes; done means fetching-token failures no longer bubble directly and are either logged with no return value or represented as a meaningful recoverable or non-recoverable state.

Vom Indexierungsmodell aus dem Issue-Text verfasst.