Definitive Edition Version: https://www.nexusmods.com/divinityoriginalsin2definitiveedition/mods/11

Adds the ability to toggle sprinting outside of combat. Sprinting can also be set to automatically turn back on once combat ends.

Four speed values are available:

• Default (50%)
• Faster (100%)
• Even Faster (150%)
• Too Fast (200%)
  

Speeds are set on a party-wide scale via the Toggle Sprint settings book. This option can only be configured by the host user.

Changelog:
Details on each update can be found on the github repo here: Changelog

To Install:

1. Unzip and place in your Mods folder (i.e. "Documents\Larian Studios\Divinity Original Sin 2\Mods" ).
2. Launch DOS2, and click the Mods button at the main menu.
3. Check the box next to Toggle Sprint.
4. Hit confirm after enabling the mod.

Important:
Given that there's now a mod to enable achievements, the loose version is outdated, and no longer supported. I recommend updating to the new version of Toggle Sprint and enabling achievements with that mod, so you can play without hassle.

Source:

The full source is hosted on Github.
I encourage you to take a look if you're interested in seeing how a basic scripting mod is done.