Brotli compression support

[Theodlz]

Don't review yet, just a draft

[Theodlz]

@stefanv I need to make some changes to the GA (like go back to the real baselayer app template not my fork) before merging anything, but this works very well! The code snippet from the GA can be reused in the SkyPortal dockerfile to install nginx with brotli :). I will also add some documentation before merging, but re-requesting a review so you can see the new code.

[stefanv]

Looks good! A few small questions.

[Theodlz]

@stefanv updated the GA and the docs to install from the ppa, and updated the python logic to find the nginx brotli module. This is solid, works well on both dynamic and static installations (and on both windows and mac).

Let me know what you think. If we want this to be tested, we will have to update the baselayer template app with a test (like the one I added to the fork pinned here for testing). So if you are happy with these changes, let me know and I'll pin the normal template app again and we can merge :)

[stefanv]

I like it! Let's also merge the test on BL.

[Theodlz]

Great! I went back to git cloning the real template app in the GA. I'll open the PR on the template app ASAP.