SIGMON-124: CI for notebooks

Context

• ticket: https://its.cern.ch/jira/browse/SIGMON-124
• The goal of the task was to introduce a CI for notebooks so all of them got executed on merge to dev or master
• lhc-sm-api merge request: lhc-sm-api!64 (merged)

What was done

• papermill_nxcals extension created and registered. (The engine omits cells tagged with 'ignore' and injects a cell with the NxCals connection configuration)
• notebooks' cells with parameters tagged with 'parameters'
• notebooks' cells responsible for creating and storing a report are tagged with 'ignore'
• test_notebooks.py which runs parametrized notebooks as tests written
• notebooks_exec job added to the gitlab-CI (based on the PoC done by Michał)
• the job which executes papermill_nxcals tests added to the CI

TODO

• There are some follow-up tasks (https://its.cern.ch/jira/browse/SIGMON-141, https://its.cern.ch/jira/browse/SIGMON-142 and https://its.cern.ch/jira/browse/SIGMON-143)

QA

• no sonar for notebooks
• code was unit tested
• acceptance tests were written (the notebooks can be treated as end-to-end tests for the api)

Review objectives

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