refactor: renovateapp.com -> renovatebot.com

lib/config/definitions.js

lib/config/templates/docker-digest-group/pr-body.hbs

lib/config/templates/docker-digest/pr-body.hbs

lib/config/templates/docker-pin-group/pr-body.hbs

lib/config/templates/docker-pin/pr-body.hbs

lib/config/templates/docker/pr-body.hbs

lib/platform/github/index.js

lib/workers/branch/index.js

lib/workers/branch/status-checks.js

lib/workers/repository/onboarding/pr/index.js

test/config/__snapshots__/index.spec.js.snap

test/platform/github/__snapshots__/index.spec.js.snap