Added documentation about using a custom CA with Docker

[AngryMandragora]

Our company is using custom CA infrastructure, and I faced the problem of either disable tls_verify or somehow use our CA certificates.
We also had newer certificates that were signed by Sectigo, which are included in the default public CA certificates, but not in the Docker image, since it uses something from 2023.
I tried to open a feature request #264, but it was not successful, so I went on figuring out how to do this.
Turns out the suggestions did not work, as the Docker image ignores the bind mounted certificate store, and you also have to set a variable for Python so the exporter actually uses the file.
Since I spent quite much time trying to figure this all out, I thought it will be useful for other people to include my findings in the documentation.

[znerol]

Thank you! Feel free to add a page to the wiki.