Update ORT website w/ 1.20.0 + 1.20.1 changes (#22768)

### Description
<!-- Describe your changes. -->
The Getting Started support matrix and ORT Release Roadmap have changed
since the ORT 1.20.0 release.

Updated w/ info about new pkgs + CUDA default version and added 1.20.1
patch release plans.


### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->