Refactoring of workflows

[drew2a]

This PR adds two new workflows:

• !PR.yml for the event on: [pull_request]
• !main.yml for the event on: [push: [branches: [main]]]

In these workflows, there are lists of child jobs that must be called for these events. It must simplify the understanding of which workflows runs on which event.

Eg:

name: Main

on:
  push:
    branches:
      - main

jobs:
  codacy:
    uses: ./.github/workflows/codacy.yml

  coverage:
    uses: ./.github/workflows/coverage.yml

  docker:
    uses: ./.github/workflows/docker-image.yml

  pytest:
    uses: ./.github/workflows/pytest.yml

All jobs besides these two are now triggered by the workflow_call event: https://docs.github.com/en/actions/using-workflows/reusing-workflows

[drew2a]

@xoriole @kozlovsky I've added ubuntu build to the !PR.yml