Packer - move to use external plugins

[mykaul]

 Warning: Bundled plugins used
 
 This template relies on the use of plugins bundled into the Packer binary.
 The practice of bundling external plugins into Packer will be removed in an
 upcoming version.
 
 To remove this warning and ensure builds keep working you can install these
 external plugins with the 'packer plugins install' command
 
 * packer plugins install github.com/hashicorp/azure
 * packer plugins install github.com/hashicorp/amazon
 * packer plugins install github.com/hashicorp/googlecompute

[mykaul]

We can of course install the correct plugin per packer image build.

[yaronkaikov]

Done as part of https://github.com/scylladb/scylla-pkg/pull/4168