chore: add size-limit

[yordis]

Description

Add https://github.com/ai/size-limit to later add the CI integration.

IMPORTANT: because of how the Github Action for size-limit works, you need to merge the dependencies and configure the CI first. The Action will clone the master version to compare the before and after, so the plugins must be available since the Action doesn't install the plugins for you. Then we could merge https://github.com/plausible/plausible-tracker/pull/41

Here is how it would look like: https://github.com/yordis/plausible-tracker/pull/1

Screenshots or GIFs (if appropriate):

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.