headers should be changed for the request, not for the client

[romanchyla]

in here: https://github.com/adsabs/ADSMicroserviceUtils/blob/master/adsmutils/__init__.py#L310

i'm surprised it doesn't cause troubles, but we might be safer updating flask.request instead of the client

[marblestation]

We want any new request that is produced as a result of processing the current request to have this header values automatically, but we do not need to alter the headers of the current request or we may mess up things (e.g., loose/overwrite information that was needed for the processing).