Use the bandwidth-file-spec.txt keywords as BandwidthFile attributes
BandwidthFile
descriptor was implemented in #29056 (closed).
Some of name of the header attributes correspond to the keywords in the bandwidth-file-spec.txt, but not all.
Since we might change the keywords, the implementation might be easier to follow the keywords using the same name for the attributes.
Currently these attributes are:
consensus_size
eligible_count
eligible_percent
min_count
min_percent
Also, measurements
should be named bandwidth_lines
according to the specification. The bandwidth lines might not be raw measurements, but scaled.