Add parent_run_id, parent_id to workflow metadata

[aryak-stripe]

Motivation

Exposing parent_workflow_id and parent_run_id in workflow executions will help with programming child workflows, and improve logging (since workflow metadata is appended to logs). This is mostly just plumbing from temporal's workflow started response.

Testing

I modified parent_workflow_spec to return the new metadata field from a child, and asserted that it was correct.

bundle exec rspec spec/
cd examples
./bin/worker
USE_ENCRYPTION=1 ./bin/worker
bundle exec rspec spec/integration

[antstorm]

Looks great @aryak-stripe ! Thank you for adding this 🙌