feat: add gzip and ungzip functions

[Vince-Chenal]

Context

Hey,

It could be useful to be able to compress/decompress payloads using gzip/ungzip functions coupled with base64 encoding (existing b64enc).

Usage example

Store compressed files within kubernetes configmaps from Helm to overcome etcd max object size limitation:

---
apiVersion: v1
kind: ConfigMap
metadata:
  name: myconfigmap
data:
  somefile: {{ .Files.Get "somefilepath" | gzip | b64enc  }}

Linked to this issue: #355

[bobh66]

This would also be very useful for templating userdata that gets passed into cloud-init via a Crossplane kubernetes Managed Resource for AWS.