docs: Toast UI Component Docs

[dgodinez-dh]

closes #874
Some thoughts from the Spectrum docs (https://react-spectrum.adobe.com/react-spectrum/Toast.html)

• Toast is in beta. Do we want to use beta components in deephaven ui?
• I tried to import Toast from our components package and does not seem to be available, so this will require a change.
• The docs say to render a ToastContainer at the root of your app, so this is another change.
• The Spectrum API passes an object of options to the queue methods. I though our code would look cleaner if those options were direct arguments in the method calls, so I wrote the documentation as such. But I am fine changing it if we do not like that idea.

[dsmmcken]

This all seems reasonable to me. Implementation looks good.

[mofojed]

This looks fine an matches Spectrum spec.
I would've thought ui.toast("blah", variant="positive") (or even just ui.text.positive("blah"))would be more intuitive/concise, but I'm hesitant to deviate from the Spectrum spec (even though it's in Beta, hasn't changed in a while). Sounds like @dsmmcken doesn't want to deviate either.

[dgodinez-dh]

Do we want to merge these docs or start implementation and then merge them?

[dsmmcken]

ui.toast("blah", variant="positive") does seem more concise, and I would support that instead if you prefer it.

Start implementation and then merge them, docs should go in at same time as feature is supported.

[dgodinez-dh]

I prefer the more concise syntax as well. We need to make changes in web-client-ui. I created this issue and assigned it to myself.
deephaven/web-client-ui#2293
Let me know if there is any problem with that.