[feature] Lack of configurable extent as default for spatial query

[luipir]

By default /search endpoint associated to Search.vue have a disabled spatial filter.
if the user enable the spatial filter, the default extent of the map to define the filter is the whole world!

Wold be fine to have a conf parameter where specify the default extent to zoom in when spatial filter is enabled:
Kind like this screenshot:

[luipir]

would be implemented with #587