client_utils: use a retrying http client

[kba]

I added those to my local fork for robustness to handle network connectivity issues. Not sure how sensible that is and hard to investigate how effective this is, so just a draft for now. If we decide it does make sense to have a retrying (and possibly also debouncing retries for more failure resilience) http client, we could generalize this.

(copied from 3b040b7a by @bertsky)