Image tags should be applied to snapshots too, optionally configurable

#### Description

The builder currently supports `image_tags`, where you can specify the tags the resulting image should have. However, the underlying snapshot that backs the image remains untagged.

Either the snapshot should automatically inherit the tags of the image, or they should be configurable separately (this seems to be how the `amazon-ebs` builder operates).

#### Potential configuration

Similar to what the `amazon-ebs` builder provides:

> snapshot_tags (map[string]string) - Key/value pair tags to apply to snapshot. They will override AMI tags if already applied to snapshot. This is a [template engine](https://developer.hashicorp.com/packer/docs/templates/legacy_json_templates/engine), see [Build template data](https://developer.hashicorp.com/packer/integrations/hashicorp/amazon/latest/components/builder/ebs#build-template-data) for more information.

#### Potential References

https://developer.hashicorp.com/packer/integrations/hashicorp/amazon/latest/components/builder/ebs