[Tune] Fix PTL tutorial docs

[amogkam]

Our tutorial for PTL is outdated: #19988

This updates the tutorial by pulling code snippets from the actual example in the docs instead of including the code snippets directly.

Closes #19988

Why are these changes needed?

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
  • This PR is not tested :(

[xwjiang2010]

Thanks Amog!