hoster image download improvements

[yaroslav-gwit]

• Store the image release date locally within the template dataset (to let user know in case there is no need to update the image)
• When hoster image command is executed - return a table with image name, release date, and image size (download size that is)
• When hoster image download https://image.link/image.zip command is executed - start downloading the image specified using the absolute link (this will allow for easier VM template sharing using GitHub, GitLab, etc etc)
• Perform zfs send | zfs receive locally if the image exists on another dataset