✏️ Fix overrides page

[ebouchut]

This PR:

• ✏️ Fixes the Overrides page
• Add an info box that matches the names in the application and the documentation that refer to the same concept. For instance, Override = Preset.

  

• Remove the Workout override section as it is not a baked-in feature of Loop,
• Adds the "Adding a Custom Override Preset" section (rework of the old Workout Override section).
• 🚚 renames the Overrides page as Presets,
• ⚙️ redirects the old overrides.md to the new presets.md page,
• ➕ adds the mkdocs-redirects plugin,
• ⬆️ upgrades dependencies,
• 🎨 Fix indentation in mkdocs.yml.

[ebouchut]

@ellenbroadman You can review what the updated page looks like here.

[ebouchut]

Later, we should revise Loop documentation to consistently use the term Preset as it appears in the application, eliminating Override.

We are not there yet.
This PR is the first step, which includes a correspondence table linking the names in the application to those in the documentation that refer to the same concept.