fix: Blocked Loading Mixed Active Content Issue Prevents Chart Viewing on Flexmeasures App

[Ahmad-Wahid]

This update addresses the problem that was preventing the viewing of charts on the Flexmeasures app. By modifying the base.html file, we now perform a check for the flask env variable. If the environment is set to production, the app will utilize the HTTPS protocol; otherwise, it will use HTTP. This adjustment ensures that the loading of mixed active content is unblocked, enabling smooth chart viewing on the app.

[nhoening]

Thanks!

[nhoening]

I just thought that this should get an entry in the changelog.

Now I am a bit stumped describing the problem.
This fixes the mixed active content issue but I don't know under which conditions this happens.
As an example, we can see charts on a PythonAnywhere server, and this issue happened GCE. What might be the difference between these? Is it the usage of Docker containers in the cloud?

[Ahmad-Wahid]

Could we access to that PythonAnyWhere hosted app from external internet?
Yes, I have deployed a docker container app and I don't think this issue would only happen on GCP. Maybe we could face it on other cloud providers too.

[Flix6x]

Deserves a changelog entry in my opinion as well.

I sometimes use ngrok http 5000 to test how UI features I'm developing would feel on a touchscreen device. It basically forwards my http localhost to a https web url, which leads to the same mixed content issue. I just verified this PR solves that for me, too. Which is great! Although I had to comment out the check for the development flask env. Why aren't we allowing this in development, too?

[nhoening]

I do believe this is likely to happen in other production scenarios, but why is PA different? Would be good to understand. We can look at the network tab on the production system and check what URL is called for this API endpoint by the asset page there...