Bump oa schema dependency to v5.15.0

[iandees]

Summary

• Update task/package.json (and lockfile) to pull openaddresses/openaddresses at v5.15.0, which adds the request.headers field to the source schema (Add request.headers field to the source schema openaddresses#8310)
• Pairs with Bump batch-machine docker image to 10.1.0 #652, which bumped the batch-machine docker image to 10.1.0 (the release that actually reads and forwards request.headers)

Test plan

• npm test in task/ passes (174/174)