Update GPU docs (#5515)

* Introduce 3 levels

Signed-off-by: davidmirror-ops <[email protected]>

* Fix ImageSpec config

Signed-off-by: davidmirror-ops <[email protected]>

* Rephrase 1st section and prereqs

Signed-off-by: davidmirror-ops <[email protected]>

* Expand 2nd section up to nodeSelector key

Signed-off-by: davidmirror-ops <[email protected]>

* Add partition scheduling info

Signed-off-by: davidmirror-ops <[email protected]>

* Reorganize instructions

Signed-off-by: davidmirror-ops <[email protected]>

* Improve clarity

Signed-off-by: davidmirror-ops <[email protected]>

* Apply reviews pt1

Signed-off-by: davidmirror-ops <[email protected]>

* Add note on default scheduling behavior

Signed-off-by: davidmirror-ops <[email protected]>

* Add missing YAML and rephrase full A100 behavior

Signed-off-by: davidmirror-ops <[email protected]>

---------

Signed-off-by: davidmirror-ops <[email protected]>