Require approval to run CI on draft PRs (#80)

By default, CI runs on draft PRs. This leads to many CI runs that may be
unnecessary.

With this PR's change to `.github/copy-pr-bot.yaml`, an `/ok to test`
comment from a trusted user is required to trigger CI on draft PRs.
Non-draft PRs will run CI by default, assuming that all commits are
signed by trusted users. Otherwise an `/ok to test` is required (as
before) -- see the `copy-pr-bot` docs at
https://docs.gha-runners.nvidia.com/apps/copy-pr-bot/ for more
information.

Part of rapidsai/build-planning#123.

.github/copy-pr-bot.yaml

@@ -2,3 +2,4 @@
 # https://docs.gha-runners.nvidia.com/apps/copy-pr-bot/
 
 enabled: true
+auto_sync_draft: false