feat: [WD-14347] Refactor for create image API

[Kxiru]

Done:

• Consolidated createImageFromInstance and createImageFromInstanceSnapshot into 'createImage'

QA

1. Run the LXD-UI:
   • On the demo server via the link posted by @webteam-app below. This is only available for PRs created by collaborators of the repo. Ask @mas-who or @edlerd for access.
   • With a local copy of this branch, build and run as described in the docs.
2. Perform the following QA steps:
   • Attempt to create an image from an instance.
   • Attempt to create an image from an instance snapshot.

Screenshots

N/A

[webteam-app]

Demo

Jenkins

demos.haus

[edlerd]

LGTM