[SIGMON-245] support signals that are mapped to the list of signals in the QueryBuilder

Context

• task: https://its.cern.ch/jira/browse/SIGMON-245

What was done

• bugfix: exploding signal column in the create_query_metadata
• utils package renamed to utils.dataframe
• custom implementation of the explode method removed (pandas one used instead with the ignore_index=True)

TODO

• test coverage should be increased - dedicated task created: https://its.cern.ch/jira/browse/SIGMON-260

QA

• sonar: http://sonar.cern.ch/dashboard?branch=SIGMON-245_multiple_signals_in_query_builder&id=lhc-sm-api
• code was tested
• notebooks passed: https://gitlab.cern.ch/LHCData/lhc-sm-hwc/-/jobs/17967048

Review objectives

• assessment of code functionality
• assessment of code quality
• identifying potential refactorings / logic common to other projects
• knowledge sharing