Added support for Key parameter in image() and svg()

[tuanvugoodmoney]

What does this change?

Add support to specify a Key for convenience methods image() and svg().

What is the value of this and can you measure success?

Clients who need to assign a key to the Image or SvgPicture could use the convenience methods like Assets.images.my_image.image(key: Key("mykey")), rather than forcing them to do something like Image(key: Key("mykey"), Assets.images.my_image).

[codecov]

Codecov Report

Merging #51 (8adf7b5) into main (1fca00d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #51   +/-   ##
=======================================
  Coverage   99.54%   99.54%           
=======================================
  Files          16       16           
  Lines         441      441           
=======================================
  Hits          439      439           
  Misses          2        2           

Impacted Files	Coverage Δ
lib/src/generators/assets_generator.dart	100.00% <ø> (ø)
...b/src/generators/integrations/svg_integration.dart	100.00% <ø> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1fca00d...8adf7b5. Read the comment docs.

[wasabeef]

@tuanvugoodmoney

Thanks for your great job.