Add SODAR proxy for IGV connections

[mikkonie]

Our SODAR use case and existing Davrods setup contain a feature to proxy SODAR request through Davrods. This is done for IGV integration to avoid the need to authenticate multiple times when opening an IGV session via SODAR.

In the existing setup this is done using SSLProxyEngine and ProxyPass:

{% if apache_enable_ssl %}
<VirtualHost *:443>
    SSLEngine on
    # ...
    {% if davrods_sodar_enable_proxy %}
    SSLProxyEngine On
    ProxyPass /__sodar/ {{ davrods_sodar_url }}
    {% endif %}
    # ...

Alas, this won't work with the current Docker image, as we intended to only provide HTTP connections in the image itself and route HTTPS with Traefik in the actual deployment environment.

To make this work would either require to set up HTTPS in Apache itself, or maybe use some Traefik trickery I'm not aware of. Suggestions are welcome.