Add option to disable profiling and task timeline

[stephanie-wang]

Why are these changes needed?

System event profiling can generate a lot of Redis data and load. This PR adds an option to disable event profiling completely. This can be controlled with the enable_timeline parameter in the _system_config (default true).

Related issue number

May mitigate #10234.

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/latest/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failure rates at https://ray-travis-tracker.herokuapp.com/.
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested (please justify below)

[rkooo567]

Looks similar to this haha https://github.com/ray-project/ray/pull/9614/files

[rkooo567]

I think we now have a better reason to make it on and off!