ETDump doc improvements

[GregoryComer]

📚 The doc issue

While enabling etdump for a custom binary following the docs (https://docs.pytorch.org/executorch/stable/etdump.html), there are a few pain points I ran into that we could potentially alleviate:

• What CMake target(s) need to be linked for etdump support?
  • Looks like it should be the etdump target.
• What CMake options should be set for the runtime build?
  • Looks like EXECUTORCH_BUILD_DEVTOOLS and EXECUTORCH_ENABLE_EVENT_TRACER?
• Include an example with the Module API, as it's slightly different.
• Document what the various MAX_PROFILING_ options do and how to set them from CMake.

Suggest a potential alternative/fix

Document the above bullet points.

cc @mergennachin @byjlw @Gasoonjia

[Gasoonjia]

thanks for sharing your thoughts!
I think all stuffs are pretty reasonable. For the first three points i will make a doc / example for them in this round of release.
For the last one im trying to find some automatic way to set it instead of manual option.