can't import v2: need semantic import versioning

with `require github.com/bazelbuild/remote-apis v2.0.0` in `go.mod`
go claims
```
go: finding github.com/bazelbuild/remote-apis v2.0.0
go: finding github.com/bazelbuild/remote-apis v2.0.0
go: errors parsing go.mod:
/workspace/go.mod:10: require github.com/bazelbuild/remote-apis: version "v2.0.0" invalid: module contains a go.mod file, so major version must be compatible: should be v0 or v1, not v2
```

with `require github.com/bazelbuild/remote-apis/v2 v2.0.0`
```
go: github.com/bazelbuild/remote-apis/v2@v2.0.0: go.mod has non-.../v2 module path "github.com/bazelbuild/remote-apis" (and .../v2/go.mod does not exist) at revision v2.0.0
```

I think remote-apis's go.mod should say `module github.com/bazelbuild/remote-apis/v2`.

cf: https://github.com/golang/go/wiki/Modules#semantic-import-versioning

Start by reading go.mod and the Go semantic import versioning guidance linked in the issue. Verify the module declaration and the two require forms against the reported Go errors; done means a consumer can resolve v2.0.0 without a module-path mismatch.

Written by the indexing model from the issue text.