[MIGraphx][Documentation] Update Documentation for ROCm 6.4 and additional MIGraphX EP variables

[TedThemistokleous]

Description

• Add info on MIGraphX EP session options controled by Provider Options or global ENV variables
• Update links to repo.radeon for ROCm 6.4 as well as support matrix
• Add descriptions for each variable used to control MIGraphX EP
• Format table to use python version number and fix formatting between available versions
• Add links to rocm/onnxruntime Dockerhub environments
• Link and reference repo.radeon.com for roll whls and other files.

Motivation and Context

Make our documentation better for users who want to use MIGraphX EP for development

[TedThemistokleous]

ping @tianleiwu @faxu @ytaous Updated documentation and added info that was missing for our session/env variables.

[causten]

Can you make a change to the Install section too. The link to Install ORT, could be better served if it pointed to the ROCm section not the CUDA part.

see comments