Allow WMS GetMap requests through the MapStore proxy

[tdipisa]

Description

MapStore is preventing you to add sources in HTTP when you are in HTTPs to avoid mixed content issues. We implemented this through #6127. This is due to a browser security constraint (eg. Chrome from v81 tries to upgrade the http request to https and blocks them by default if they fail to load over https, see also here).

Through this issue it is requested to let certain OGC requests (like GetMap requests) to pass through the MapStore proxy.

Acceptance criteria

From our preliminary tests the proxy should already work for the purpose of this task. Anyway there, given the proxy is ok we need to:

• Allow to add catalog in http-not-secure
• Allow WMS layers to load tiles
• Do not support other type of protocol for the moment (TMS, WMTS... ) because these require additional work on specific implementations

In order to support what requested for this task, we need to change several things here and there on MapStore UI:

• Add a flag in the UI of advanced options of catalog of type WMS and WFS. Let's call it in the UI "Allow not secure layers". Option in catalog should be "allowUnsecureLayers"
• A WFS layer, with the fix above, should work. To be checked
• Also WMS with Cesium should work, because they already use the proxy. To be checked
• In case a WMS layer has been added using a catalog, a flag forceProxy: true option in the layer should be added. This option forces the layer to use the proxy and load the data, instead of doing a direct request. Only Openlayers supports this parameter, Leaflet doesn't, therefore mobile maps will not work if that option is set to true

This option has to be :

• Documented on MapStore
• Saved in map (there is a filter of savable options) and so restored in a second time when the map is loaded
• Fixed in implementation (Openlayers has some implementation but is partially overridden by other things, so it is not fully working).
• The flag should be added to the display tab of layer setting to allow to enable/disable in a second time at layer level

Other useful information

Services to test:
http://www.rendis.isprambiente.it/geoserver/wms
http://www.rendis.isprambiente.it/geoserver/wfs