Markdown linting: Make targets and add markdownlint-cli2 as a mise dependency

Why is this change being made?

This adds two Make targets to make local markdown linting easier:

make lint  # lint all markdown files
make lint-changed  # lint only changed markdown files as compared to main branch

We also add markdownlint-cli2 as a mise dependency, so we can install the linter through a simple mise install.

The relevant documentation update is docsy-gitlab!119.

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Commits

• Add markdownlint-cli2 as a mise dependency

This makes it easier for everyone using the linter locally and therefore aims to speed up feedback cycles.

Documentation update in docsy-gitlab!119

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