Review bandwidth history parsing in ExtraInfo descriptor parser class

The code we are using to parse bandwidth history from ExtraInfo descriptor is taken from the stats module in the current metrics website. There we have some dirty hacks that are used to linearly distribute intervals and bandwidth values (https://gitlab.torproject.org/tpo/network-health/metrics/website/-/blob/master/src/main/java/org/torproject/metrics/stats/bwhist/RelayDescriptorDatabaseImporter.java#L298).

I think this was specifically needed because we had to write values to the DB in a format that could be easily interpreted as a time serie.

I also think we can review this code now, and maybe take the onionoo approach for example where we just write the interval and the bandwidth value:

https://gitlab.torproject.org/tpo/network-health/metrics/onionoo/-/blob/master/src/main/java/org/torproject/metrics/onionoo/docs/BandwidthStatus.java#L229