set the channel topic: Working group for custom GPU types

set the channel description: https://github.com/flyteorg/flyte/discussions/3796

@Ketan (kumare3) for naming suggestions - thinking about adding this field. okay? https://github.com/flyteorg/flyteidl/pull/419/files#diff-8bd2613bf781125f77247c29a2f5502658c63cccf2b597a9ec3695ef1e7b2ca9R37

background - the reason for adding an additional field rather than a custom resource enum, is that we are thinking the UX on the front-end will look something like

@task
def t(requests=Resources(gpu="1", gpu_type="A100")): ...

or something like that.

cc @Andrew Dye