document missing functionality and print warnings / raise errors where needed

[OriHoch]

it seems there is some missing functionality in some functions - e.g. methods which were not implemented or are not supported for Kamatera

Please:

1. document in the README all the missing functionality
2. where possible - raise an exception / error - for example, in case of delete artifact - there should be an exception as user expects artifact to be deleted but in fact they are not deleted.
3. if not possible to raise an exception / if it prevents other functionality from working / if the functinoality is not necessary - print a warning to the user

examples of such places:

• https://github.com/Kamatera/packer-plugin-kamatera/blob/main/builder/kamatera/artifact.go#L20
• https://github.com/Kamatera/packer-plugin-kamatera/blob/main/builder/kamatera/artifact.go#L36