Defining an environment for the ew-analyses repository

The lhcb-qee/ew-analyses> repository defines a common framework to do EW studies at LHCb. It currently defines a custom way of setting up the environment based on a LCG version and platform together with a few additional python packages. After a presentation at the PPG meeting it was decided to try using lb-conda in order to handle the environment as well as providing the desired functionalities to fully test the analyses in the CI. The current implementation relies on lhcb-docker/analysis-ci> in order to produce suitable images that mimic the lxplus environment, and the Kerberos key from the analysis and preservation team in order to access EOS.