Automatically upgrade old filters instead of requiring —force

[sinbad]

Came across a case recently where someone hadn't used git-lfs for a while and suddenly got errors on git lfs install of the form:

filter.lfs.clean attribute should be "git-lfs clean --%f" but is "git-lfs clean %f"

This surprised me because I thought we had upgrade paths for our config, but turns out that was only for hooks. So rather than making them run git lfs install --force for something we already know about, I introduced the same concept as for hooks, a list of upgradeable values we used to use.

While I was at this I removed the attribute upgrade path for git-media, since it was vague and over-general really and I don't think it's necessary any more? I can put it back if there was a specific reason it's still there but looked like a relic to me.

[technoweenie]

Awesome, thanks for adding this!

The git-media stuff is way outdated. I don't think there's any need to find every filter we used during development :)

[ttaylorr]

This looks awesome. Thanks!