[v2] E2E test groundwork

[blampe]

This adds the groundwork for e2e testing the v2 branch. Try it with make test-e2e.

• The Kubebuilder scaffolding was expecting some kustomize files on top of operator/config, so I regenerated CRDs into operator/config/bases and dropped a Deployment into operator/config/manager. We'll eventually need to consolidate this with the root config/crd.
• I happened to have a more recent version of protoc-gen-go-grpc which changed the generated code slightly. I checked in a .mise.toml mostly just to write down which versions of each tool I was using while working on this. Totally optional but you can read docs here if you'd like a direnv-style tooling setup.
• I removed the agent's Dockerfile, so we now have one image with manager and agent binaries.
• I added a make target to build the rootless repo. I think we'll still want to get this working with the root repo.
• I had to cut some corners with the image's version tag and how that gets plumbed to the agent. I'm currently generating a random hex tag and baking that into the binary to guarantee the operator spawns agents using the same image.
• I copy-pasted some of the scaffolded RBAC stuff to get leader election working. The operator doesn't do any cleanup so it should be safe to relinquish the lease on shutdown.
• Simplified the scaffolded e2e test -- we don't need prometheus or cert-manager (yet -- if we do we can add them later).

I haven't enabled an assertion for the random-yaml stack because I wasn't able to see it reliably reconcile. I was seeing GitHub rate limit errors as well as errors from the operator when updating status on the stack.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 16.00000% with 21 lines in your changes missing coverage. Please review.

Please upload report for BASE (v2@e850d02). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
agent/pkg/proto/agent_grpc.pb.go	0.00%	19 Missing :warning:
operator/cmd/main.go	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## v2 #665 +/- ## ===================================== Coverage ? 19.06% ===================================== Files ? 25 Lines ? 3745 Branches ? 0 ===================================== Hits ? 714 Misses ? 2925 Partials ? 106 ```

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