Improve store bulk and app bulk topic descriptions

[nickwesselman]

Summary

Fills in store:bulk and app:bulk topic descriptions in packages/cli/package.json. Without an explicit entry, oclif falls back to the first subcommand's description, which for both topics happened to be cancel's — misleading since the topic also contains execute and status.

Before

store bulk    Cancel a bulk operation on a store.
app bulk      Cancel a bulk operation.

After

store bulk    Run, check, and cancel bulk Admin API operations on a store.
app bulk      Run, check, and cancel bulk Admin API operations for an app on a store.

Test plan

• node ./packages/cli/bin/dev.js store --help shows the new store bulk description
• node ./packages/cli/bin/dev.js app --help shows the new app bulk description