Use a layer extent

[JulesGrillot]

Feature description

Add a QgsMapLayerComboBox to select a layer in the project and use is extent.

Needs to transform layer's extent to right crs.

Add possibility to select either the layer's extent or the layer's geometry as filter to fetch wfs data

Additional context

No response

[JulesGrillot]

Layer combobox added, layer extent fetched. Need to add a checkbox to give choice for filtering data with Intersects or Within extent.