Allow the Kubernetes agent to be registered with a pre-install hook

[liam-mackie]

Background

As a part of the Kubernetes Monitor, we need to have the Kubernetes agent registered prior to the agent registering with server. To do this, we need to run a pre-installation script.

To keep this backwards-compatible, we can't touch any existing resources, or helm may delete files that have data in them.

As such, we have opted for the pre-installation hook to write the configuration to a different configmap and secret, and have created a new command in tentacle to migrate the configuration to the final destination.

Results

• There's a new command in Tentacle which copies the data from the pre-installation configmap and secret and overwrites the destination data to use it
  • This should only ever happen if the agent was not registered in the existing configmap
• There's a new script that's been added called register.sh which only runs the registration commands.

There should be no change to existing behaviour without additional changes to the helm chart to enable it.

I've also fixed up some of the integration tests to escape paths that may have spaces to fix issues running them on MacOS.

How to review this PR

Quality ✔️

Pre-requisites

• I have read How we use GitHub Issues for help deciding when and where it's appropriate to make an issue.
• I have considered informing or consulting the right people, according to the ownership map.
• I have considered appropriate testing for my change.

[eddymoulton]

Couple of small test things but other wise looks good