GSLUX-664: Proxyurl as a setting from v3

[AlitaBernachot]

JIRA issue

https://jira.camptocamp.com/browse/GSLUX-664

Description

• Created a new helper ProxyUrlHelper
• Allow initialization of ProxyUrlHelper through ProxyUrlHelper.init_v3() with some params (⚠️ To be used only in v3, this function should be removed when v4 is fully ready)
• Default params are declared in new .env: VITE_USE_PROXYURL, VITE_PROXYURL_WMS, VITE_PROXYURL_REMOTE

Don't know if adding a .env is the best idea, if there are some app settings to be configured, a settings.json (loaded with import settings.json) could be better. But this can be improve in another PR.

This PR is linked to Geoportail-Luxembourg/geoportailv3#3133

[github-actions]

GitHub Pages links: * Luxembourg-geoportail: https://geoportail-luxembourg.github.io/luxembourg-geoportail/GSLUX-664-proxywmsurl/

[mki-c2c]

works well.

I just wonder if we shouldn't use a store instead of a global object for more genericity.

and there seems to be a typo in the test launch command

[mki-c2c]

shouldn't we use a store for the proxy properties ?
Changes need not be monitored, but it will be more consistent with other "global variables" saved as a state in a store

[AlitaBernachot]

At first, I put the variables in a store. But I wasn't convinced after a few tests because:

• proxyurls vars never change, they depend only on the env the app is launched on
• if it is comming from a store, it means: the helper should only be used inside a vue component OR the helper should be used once the store is fully initialized (with the right values). It can be done using watch() in v3, but sometimes the layers are created before the init of the proxyhelper, I have no control on that (too complicated for now).

So I made it simple, because these urls never change and they depend on the environment, I put them as environment variables.

I have made some changes on the Proxyhelper to make it clear that initialization is needed only because we need to retrieve environment vars from v3, otherwise initialization in v4 is pointless.

Also, I remember we have discussed about a potential configuration store last year, maybe later this can be moved into this future store when we have time.