feat: prCommitsPerRunLimit (#4392)

docs/usage/self-hosted-configuration.md

lib/config/definitions.ts

lib/platform/git/storage.ts

lib/workers/branch/index.js

lib/workers/global/index.js

lib/workers/global/limits.ts

lib/workers/repository/process/write.js

renovate-schema.json

test/workers/global/index.spec.js

test/workers/global/limits.spec.ts

test/workers/repository/process/write.spec.js