Bigtable's `scantest` and `loadtest` tools rely on Config

[telpirion]

Related:
googleapis/google-cloud-go#6124

Environment details

• OS: Any (tested macOs)
• Package version: v0.12.0

Steps to reproduce

1. Run command go install cloud.google.com/go/bigtable/cmd/loadtest@main

Expected behavior

Install succeeds.

Actual behavior

Install fails because of dependency on cbt.

[Capstan]

I have an import pr stalled in the Google monorepo blocked on this.