Find a tool to automatically detect (or propagate) major version changes through the workspace

When we bump the major version of `wkt` or `gax` (or any generated client that is a dependency of another) we need to change all the downstream dependencies.

`cargo semver-checks` does not detect the breaks, as documented in #3237. Maybe `release-plz` can do this job, or `cargo-workspaces` can do the job, but we need to test them (I cannot figure out how to do that easily safely).

For now, we will add a GHA step using shell + awk. Moving that to a Go or Rust tool would be an improvement. Writing our own set of `cargo` helpers may be what we need in the long term.