onnxruntime

Expand the documentation on using compiling EPs with a minimal build (#5893)

* Expand the documentation on using compiling EPs with a minimal build to call out a 'simple' option that is easier to use. Provide more background on what happens to help users choose the best option for them.
Tweak conversion script to be noisier about attempted usage of 'all' optimization level.

Co-authored-by: manashgoswami <magoswam@microsoft.com>