Overhaul group and widget sizing options

### Description

Our current sizing widget allows a user to select from `auto` or an `x` by `y` size for a given group or widget. This was inherited from Dashboard 1.0, and to-date has provided enough functionality to get off the ground. However, there are more flexible options here that I think we should consider, in particular a separation of `x` and `y` sizing.

Consider the following:

- `auto` in a single dimension. Currently, the `auto` option fills the horizontal space (`fill-container`), and then vertically adjusts to it's content (`hug-contents`). In some cases, you may want to have a defined width, but fill whatever space is available vertically.
- Introduction of "Fill Container" and "Hug Contents" options for each dimension as "auto" (as mentioned int he previous point) does have inconsistencies.
- If a group is given the "Fill Container" option, then we would easily be able to produce full-screen widgets, e.g. charts or worldmaps

### Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate