Add support for .mailmap files

[patrickdevivo]

See here for context. It would be useful to be able use mappings in a .mailmap of a repo to de-duplicate authors in queries.

I'm not entirely sure how we add support for it - maybe as a helper function that takes the contents of a .mailmap and an email address, and returns the associated name.

Something like SELECT mailmap(<mailmap-contents>, 'some@email.com')

[chrisma]

It might also be an idea to represent the .mailmap file as a DB table itself, that could be written and queried.
If a query is executed that is marked as using this mailmap table, contributors would be merged. That is how the git CLI does it. When a .mailmap file is found, all further commands respect it by default.

This could mean that the mailmap config would only have to be setup once for a repo, and no additional helper functions would clutter the SQL code.

An SQL query could then be constructed that identifies those email addresses in the current contributor list of the repo, which have not yet explicitly been handled in the .mailmap file (i.e. don't have a canonical name assigned)

[patrickdevivo]

First version handled in this PR: mergestat/mergestat#250

[chrisma]

Very cool! 👏

[chrisma]

I've added my idea of representing the contents of .mailmap as a table in MergeStat in a separate issue (#254) in case that's of interest