Majority of the NGINX config is the same, for both HTTP and HTTPS.
Having two separate templates for them is making configuration changes
error-prone, where we often risk forgetting making the same change in
the other file.
This PR merges the two files into one, so the above risk isn't there. It
also makes it easier to experiment with the file while developing, since
we have to make every single change twice during development.
Note: This _will_ cause conflicts in sync, after being merged.
Why are we doing this? This will be a step towards simplifying our
`Dockerfile` with reduced layers and improved caching performance. The
image build time in CI should be faster once this is done.
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