Make setup-tools runnable locally

[blampe]

It can be very difficult if not impossible to get a local environment to look the same as the environment we use in CI, with all of the relevant toolchains and dependencies installed at the correct versions.

This can make it really difficult to debug issues in CI, especially if the problem boils down to something like changes in a language toolchain's version.

Ideally, developers and CI should be able to share the same setup steps.

Proposal

As a starting point, I'll suggest we experiment with something like mise:

• Website
• GitHub action

This is similar to asdf with nicer support for Go tooling -- helpful considering all of the small programs we use as part of our workflows. Unlike nix, dev containers, etc. it doesn't require Docker/sudo so it's usable locally, as well as on CI and in other places like our Renovate worker.

As part of setup-tools we can check if a project has a .mise.toml defined (example -- here the operator specifies the protoc version it needs), and if it does use that to setup all the tools:

- name: Run mise
  if: ${{ hashFiles('.mise.toml') != '' }}
  uses: jdx/mise-action@v2
  with:
    ...

Other benefits:

• This caches all of our tools, which speeds up setup and preserves things like previously downloaded packages.
• Renovate can natively manage .mise.toml, so the problem of toolchain upgrades -- currently handled via action versions in ci-mgmt -- can instead be handled (more appropriately) by the provider itself. This would, for example, reduce our maintenance burden from long-tail providers: it would be possible to allow a provider to stay on older versions of Go, or golangci-lint, etc., for example, instead of forcing someone to manually resolve incompatibilities across all of our providers whenever we want to upgrade something.