Use much faster "ort" strategy for rebases and merges

[bablex]

Since git 2.31.0 git has a "ort" strategy (-s ort) which is 500-9000x faster than the current default.
Please use this strategy by default (or give an option to enable it for merges and rebases in the settings).
I'm using it via the git CLI already, and it's incredibly fast, but would like to have it via the "Merge" button and "Rebase" context menu option too.

EDIT: see https://github.blog/2021-08-16-highlights-from-git-2-33/#merge-ort-a-new-merge-strategy for details