Feature request: support clean as a top-level option in buf.gen.yaml (v2)

Feature request: support clean as a top-level option in buf.gen.yaml (v2): a task in MiMo-V2.6-RL-harbor-code: MiMo-V2.6-RL Code (Harbor) (Harbor dataset). Right now the only way to wipe plugin output directories before code generation is the --clean flag on buf generate . There's no equivalent in…