support adding additional tag(s) to the targets

[briantist]

I want to be able to specify a new tag or tags that will be set (in addition to the existing ones) when syncing.

For example something like this:

target:
  host: ghcr.io
  repository: briantist
  additional_tags:
    - stable-2.11
sources:
- repository: ansible/base-test-container
  host: quay.io
  tag: 2.1.0
- repository: ansible/default-test-container
  host: quay.io
  tag: 5.4.0

So that the two source images would get synced to the target with both their original tag, and the additional tag(s) entered, like ansible/base-test-container:2.1.0 would also be ansible/base-test-container:stable-2.12.