[WORK IN PROGRESS] SEO

This is the current state of the SEO efforts on the client side. It's based on https://github.com/geoadmin/mf-geoadmin3/pull/1123 and will be used by https://github.com/geoadmin/mf-chsdi3/pull/418

In addition, it currently has the following functionality:

- Adapts the apache configuration to re-direct bot traffice to the snapshot service (note: this has not yet been tested on main). This needs the snapshot service to be existant in the api url
- Add metadata of layers specified via 'layers' parameter.

Specify snapshot=true in url to see the effects.

I would like to test the apache re-direction in main. Maybe we can do this tomorrow?