Introduce Code Documentation Workflow Dependent on CMake Workflow

[franziska-wegner]

This PR separates workflows by task such that they become reusable [7], e.g., the cmake workflow which content is required and duplicated in the other workflows will run in the end only once. This will save computational power and time in the end. There are different events that may trigger workflows given in [6]. Another option is to call the workflows in the main workflow directly [8]. For the two former options there is a big difference in reusability of the dependent workflows. It is worth testing the context reusability of both versions (see below).

Advantage:

1. Reuse results and workflows [7],
2. Consume less computational resources,
3. Build does not fail multiple times,
4. Gives the workflow structure and gives them a better granularity,
5. Reduces the workflow size,
6. Simplifies adding new workflows.

Unfortunately the dependent workflows do not inherent the whole environment. As such we need to make sure to maintain the build directory and the installations for the upcoming workflows. There are two approaches given by GitHub, (1) Caching, and (2) Artifacts. A docker solution is also given in [8].

Caching makes more sense in our case as we need the result directly and only for the workflows that depend on a particular workflow, i.e., the build directory is not a long living artifact, but a short term object only required for the dependent workflows [4]. The caching approach is also less time consuming and thus, preferable.

In total, we add and modify the following files to have the resulting dependency graph:
modified: .github/workflows/cmake-multi-platform.yml
new file: .github/workflows/code-documentation.yml

[1] https://docs.github.com/en/actions/using-workflows/caching-dependencies-to-speed-up-workflows
[2] https://docs.github.com/en/actions/using-workflows/storing-workflow-data-as-artifacts
[3] https://docs.github.com/en/organizations/managing-organization-settings/configuring-the-retention-period-for-github-actions-artifacts-and-logs-in-your-organization
[4] https://levelup.gitconnected.com/github-actions-how-to-share-data-between-jobs-fc1547defc3e
[5] https://stackoverflow.com/questions/58457140/dependencies-between-workflows-on-github-actions
[6] https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#workflow_run
[7] https://docs.github.com/en/actions/using-workflows/reusing-workflows
[8] https://stackoverflow.com/questions/57498605/github-actions-share-workspace-artifacts-between-jobs

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (cb587f8) 94.37% compared to head (dc79edb) 94.37%.

Additional details and impacted files

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  Coverage   94.37%   94.37%           
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  Files          49       49           
  Lines        4921     4921           
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  Hits         4644     4644           
  Misses        277      277           

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