Flip CAPI support to disabled by default

[foot]

Partially addresses #3658

Other issues to address:

• [user-guide] Update the user-guide to show how to enable CAPI
• [user-guide] Add a page about disabling / enabling CAPI support + restarting deployments
• [user-guide] Make it more explicit that Policy still requires cert-manager (which is often implicitly installed with a capi-provider)

What changed?

• Flip CAPI support to disabled by default
• Also remove the explicit ".enabled: true" options in the values.yaml.

Why was this change made?

• Also remove the explicit ".enabled: true" options in the values.yaml.

You cannot actually disable any of the controllers without a lot of things breaking. This reduces the visibility of this option and discourages users for playing with it.

How was this change implemented?

Parts of the system that recognise global.capiEnabled

1. cluster-service: if capi is enabled then capi cluster details are queried for and returned in the /v1/clusters endpoint
2. cluster-controller: if capi is enabled then capi clusters status is used to calculate the gitopscluster status

How did you validate the change?

• Explain how a reviewer can verify the change themselves
• Integration tests -- what is covered, what cannot be covered;
  or, explain why there are no new tests
• Unit tests -- what is covered, what cannot be covered; are
  there tests that fail without the change?

Release notes

Documentation Changes

Other follow ups