Search service: Fix dependencies

Use pipenv, add missing dependencies and fix README

Previously the search-service had missing dependencies, resulting in a failing setup locally. The command to setup and run the service was also wrong in the README file, as it caused the dependencies to be installed system-wide.

This MR fixes all of the above problems. Once merged, it is recommended to rebase all relevant branches to completely eliminate this problem.

requested review from @mweise

assigned to @spannringm02

requested review from @spannringm02 and removed review request for @mweise

@spannringm02 please review and check if this is ok for you

works fine for me

mentioned in commit 606fffd8

merged