[v2] protoc required to build dbt v2

### Is this a new bug in dbt v2.x compared to the latest version of dbt 1.x?

- [x] I believe this is a new bug in dbt v2.x
- [x] I have searched the existing issues and could not find a duplicate

### Current Behavior

A protoc dependency is required to build dbt v2, which is not specified in any documentation, installation scripts, etc.

We should likely not have a full dependency on protoc period. Assets could be checked in and the dependency could be required only to refresh clients / protobufs.

### Expected Behavior

Either (1) installation is documented and easy or (2) remove protoc dependency.

### Steps To Reproduce

`cargo build`

### Relevant log output

```shell

```

### Environment

```markdown
- OS:
- CPU: (x86 or ARM)
- dbt distribution and version: (`dbt --version`)
```

### Which database adapter are you using?

_No response_

### Is this a discrepancy vs. dbt 1.x?

- [ ] Yes — this works in dbt 1.x but not in dbt v2.x

### Additional Context

_No response_