Migrate the dashboard grid to React

[arikfr]

https://github.com/STRML/react-grid-layout might be relevant here.

Part of the React migration (#3071).

Blocked by #3301.

[ranbena]

react-grid-layout seems like best choice.

@arikfr any functionality improvements you'd like to add?
e.g Skeleton widget loading to prevent initial clunkiness (jumpy widget heights).

[arikfr]

As with any migration, it's best if we focus on porting current functionality before doing any improvements. If there are some quick wins that can be added on the way, then sure.

Reducing the minimum "step" size could be nice, but it has implications on existing widgets, so not sure about it.

[kravets-levko]

Reducing the minimum "step" size could be nice, but it has implications on existing widgets, so not sure about it.

It will just require migration to update existing widgets (sizes and positions).

[ranbena]

Closes #1775.

[arikfr]

@ranbena I think that #1775 is more about widgets in general, like UI components. Anyway, not relevant anymore.