Support git.similarityThreshold

[ledenis]

Since VS Code 1.79 (May 2023), there is a setting called git.similarityThreshold that is used for VS Code Source Control view. (Source). However, Gitlens uses its own setting called gitlens.advanced.similarityThreshold.

We could align Gitlens to use git.similarityThreshold instead of gitlens.advanced.similarityThreshold, so that users don't need to set it in two different places.

Moreover, the possiblity to use a VS Code setting for it was mentioned here #1469 (comment) back in April 2021:

Maybe it is best to open an issue for VS Code to add a similar similarityThreshold setting, and then GitLens could align to use that setting, so it would work across the board.