[feature request] Add support for Plausible analytics

Hi, I'd like to propose to include support for privacy friendly Plausible analytics in gancio.

Reasoning: we are starting to use Gancio for a community calendar and although we are very privacy friendly, we still would love to see at least some analytics for the website.

Proposal details:

• Plausible Analytics: https://plausible.io
• Integration guide for vue-nuxt apps: https://plausible.io/docs/integration-guides#vuejs--nuxtjs

User stories:

• Configuration story: As an instance administrator, I need to be able to edit and save all important fields of Plausible analytics integration as described here - https://github.com/moritzsternemann/vue-plausible#usage - we are using self-hosted plausible analytics instance, so we need to direct the analytics there.
• Analytics story: As an instance owner, I'd like to see usage statistics for publicly visible routes - main page, static pages and details of events. Admin routes don't need to be tracked.

Some other notes:

It doesn't seem to be a large effort - documentation seems pretty straightforward. Unfortunately, I am not a programmer to try to build the project with analytics myself, update the gancio templates and add new config section for admin routes.