Add support to install CloudNativePG and it's plugin

[sxd]

CloudNativePG it's a PostgreSQL operator for Kubernetes which relies entire on Kubernetes API to take actions over the PostgreSQL cluster, also provides a plugin to manage the clusters and backups.

Expected Behaviour

The expected behavior will be to be able to install the operator inside the target kubernetes cluster and also being able to install the plugin as an app,

Are you a GitHub Sponsor yet (Yes/No?)

• Yes
• No

Possible Solution

I would like to create a PR to install both the plugin and the operator, but I would like to start with a PR for the plugin and then going forward with the operator, but I don't know if that's the right path to follow or there's something else we should do to add it to the market

Context

The main idea here it's promote CloudNativePG and make it easy to install it for Arkade users and in the process promote the use of the operator and plugin for users, since the plugin it's a powerful tool but people usually find really hard to install it

If requesting a CLI for "arkade get"

How many downloads does this tool have? Check at:
https://somsubhra.github.io/github-release-stats/?username=cloudnative-pg&repository=cloudnative-pg&page=1&per_page=5
Total Downloads117,457

Your Environment

CloudNativePG supports Kubernetes 1.23 to 1.26

[alexellis]

Feel free to go ahead and work on a draft PR @sxd