[Canvas] Ability to zoom in/out on a workpad

[ryankeairns]

Describe the feature:
Similar to other presentation and vector editing tools, provide a workpad zoom in/out feature that only zooms the workpad itself (as opposed to native web browser zooming which makes all elements smaller/larger).

Consider using the Z key to toggle zooming and, once active, hold down Ctrl (then click on workpad) to zoom out.

Shortcuts:
zoom in:
cmd+option++ (mac)
ctrl+alt++ (windows, linux, etc)
zoom out:
cmd+option+- (mac)
ctrl+alt+- (windows, linux, etc)

Describe a specific use case for the feature:
We have a lot going on around the workpad (global Kibana top nav, Kibana side nav, Canvas top bar, Canvas bottom bar, Canvas right-side settings panels), all of which restrict the workable area for the workpad.

Much (all?) of those surrounding areas are often required to be visible (or would require redesign), so a zoom capability provides a quicker path forward.

[elasticmachine]

Pinging @elastic/kibana-canvas

[ambigus9]

+1 to this request.

[cqliu1]

Merged in #38832.