feat: Add prcreation == approval (#4032)

lib/config/definitions.js

lib/workers/branch/index.js

lib/workers/pr/index.js

lib/workers/repository/master-issue.js

lib/workers/repository/process/index.js

lib/workers/repository/updates/generate.js

renovate-schema.json

test/workers/branch/index.spec.js

test/workers/pr/index.spec.js

...pository/_fixtures/master-issue_with_3_PR_in_approval.txt

test/workers/repository/_fixtures/master-issue_with_8_PR.txt

test/workers/repository/master-issue.spec.js

...rs/repository/updates/__snapshots__/generate.spec.js.snap