Ability to Update Tags in "az sig image-version update" and "az sig image-definition update"

**Related command**
az sig image-version update
az sig image-definition update
az sig ... update

**Is your feature request related to a problem? Please describe.**
I would like to request a feature enhancement for the Azure CLI commands related to Service Image Gallery. Currently, the commands "az sig image-version update" and "az sig image-definition update" do not provide an option to update tags for existing images or image definitions. This option is available in the GUI interface.

**Describe the solution you'd like**
I would like the ability to update tags directly within the "az sig image-version update" and "az sig image-definition update" commands. This enhancement would allow users to modify tags for image versions and definitions programmatically, streamlining image management workflows and enabling more efficient automation.