setup a dependabot dependency group for wgpu-related updates

See https://docs.github.com/en/code-security/dependabot/working-with-dependabot/dependabot-options-reference#groups--

open wgpu related crates PR together instead of one by one
- for major versions
- for `wgpu`, `wgpu-types`, `naga`, `naga_oil`, `dlss_wgpu`