Mapserver certificate download

[juagargi]

Currently, the main method of ingesting the CT log server certificates is via the ingest CLI.
However, the mapserver is able to download the certificates all by itself.

This is a meta issue for the following:

• Review the correctness of the mapserver downloader.
• Study its performance, in terms of certificates per second that is able to download.
• Create backup copies, akin to the .gz files we create now before running the ingest CLI.
• Run the mapserver downloader for a month and check for bugs.