Make it possible to customize openlayers

[maltaesousa]

Since the upgrade to Django 5.1, the old way of customizing OpenLayers widget in the admin is not working anymore. This PR makes it work again but in a better way by using a plugin and not by "hacking" the template as it was done before.

For now, it is possible to change the background layer and replace it with a WMTS. By default, swisstopo backend is used:

all the config is done in the settings.py

[hbollon]

Hello @maltaesousa !
I don't think I can help with this PR sadly, I'm from Infrastructure department of Camptocamp and I'm helping GS for K8S/Docker/CI/Automation stuff but I'm not really qualified on Geospatial/openlayers topics 😞
That said I still can help with Frontend/Backend as long as it doesn't really require geomatics skills 😄

[marionb]

Hi @maltaesousa
Thanks for the PR. I just got back from vacations this week. I will take a look at your PR this week, I reserved some time on Thursday morning to do a review.

[marionb]

Hi @maltaesousa
sorry for the delay but the PR looks good and works locally. After a rebase this is good to be merged.
Thanks!

[maltaesousa]

Thanks @marionb ! It was my time to be back from vacations :)