[C++ Worker]Ignore genrated files

[qicosmos]

Why are these changes needed?

C++ worker will generate a template project, we need to ignore the generated files by c++ worker.

Related issue number

Checks

• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests

[SongGuyang]

LGTM.

[kfstorm]

CI failures are unrelated.