Add update types for Cargo-style (in)compatible version upgrades

[jwodder]

Is there an existing issue for this?

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Feature description

Currently, the only options for update-types in dependabot.yml are "major", "minor", and "patch", all defined as per SemVer. However, Cargo (the Rust package manager) uses a modified form of SemVer in which "Versions are considered compatible if their left-most non-zero major/minor/patch component is the same." Thus, a version upgrade from v0.1.0 to v0.2.0 is considered "incompatible" even though, by typical SemVer standards, it is minor.

I therefore request that ignore.update-types and groups.*.update-types gain support for the options cargo-compatible and cargo-incompatible (just spitballing on the names) for ignoring/grouping (in)compatible version updates.