rationalize column headers across CSV output files

[ctb]

prefetch and gather use different CSV column headers for their output, and I'm sure so does search and other commands.

Would be good to fix this in v5.

[ctb]

might want to include duplicate columns for backwards compat... everything in genome-grist and charcoal will break if we swizzle the names 😆

specific example: gather output has name, prefetch output has match_name. Grr.

[ctb]

I was thinking that a ~clean way to do this would be to add two options, one to use current column names (default in v4.x) and one to switch column names (new); then swizzle the defaults for v5, and deprecate the current column names in 5; and then remove the old column names in v6.

[ctb]

starting to work on this: https://hackmd.io/EdrdrkByQ7a2GuyiN5oyGQ and #2274

[ctb]

note, docs requested for ANI columns 😓 #2367 (comment)

[bluegenes]

note that we should now also update these in the rust layer, e.g. https://github.com/sourmash-bio/sourmash/blob/latest/src/core/src/index/mod.rs#L57-L64