Get Bounds/Extent of COG Source

[DanielJDufour]

Is your feature request related to a problem? Please describe.
A user may want to display a box around the extent of the GeoTIFF or zoom to the GeoTIFF when it is loaded

Describe the solution you'd like
A clear and concise description of what you want to happen.
var extent = await source.getExtent();
This will have to be a promise.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.