Dependabot configuration fixes

1. Group all updates to a single PR
2. Minor/patch version updates only unless there's a security vulnerability

https://github.com/Azure/azure-sdk-for-rust/pull/3761#issuecomment-3916472545

> Still, we shouldn't be upgrading dependencies "just because". @danieljurek will look into proper configuration. We only upgrade dependencies for security updates or if we need functionality. Though cargo and rust in general can compile and link multiple versions of a dependencies, this isn't always the default behavior nor ideal to optimize binary size or possible bad interactions with multiple versions.