Add codespell action and workflow for spell-checking (OSOE-960)

[Piedone]

Add an action and a reusable workflow to do spell-checking with codespell.

Codespell works by looking for misspellings (like these) instead of matching every word to a dictionary. While this is surely a less safe approach if the ultimate goal is to prevent spelling mistakes, it also looks like one that would basically eliminate false positives. This is a better deal than having frequent annoying false positives, even if this means that a few misspellings may slip through.

We could use the codespell GHA action, what installs codespell and runs it. However, this is only a quite thin wrapper on the codespell executable, doesn't use the latest version of it, and doesn't expose all config options (like codespell-project/actions-codespell#19 and codespell-project/actions-codespell#63) that we might need. So, perhaps just use it from PIP by doing something like this.

• Add an action and a reusable workflow. The action should run codespell from the CLI.
• The action should contain a default configuration suitable for most of our projects, with options to override what's necessary. Using a custom config file in the consumer repo should be possible.
• It should be possible to exclude any number of complete files and folders, also by patterns (so we don't check all OSOCE submodules in other superprojects).
• Display a hint/message on failing spell-checking with information about where to find documentation, and how to ignore single false positives inline.
• Add Markdown documentation.
• Add a job to the Build and Test workflow of OSOCE, like there is Spelling now, that we'll run in parallel as a test for now.
• Contrast the number of false positives of check-spelling and codespell. How many inline ignores and dictionary entries? Also in the other projects.

Jira issue

[Piedone]

In OSOCE, check-spelling produces 112 false positives, while codespell 10. In LGHA (including the common defaults), this is 242 vw 10.