Add CRUD support for spaces groups

[RedbackThomson]

Description of your changes

Rebased on top of #457

Add support for up group create/list/get/delete using the selected spaces kubeconfig.

I have:

• Read and followed Upbound's contribution process.
• Run make reviewable to ensure this PR is ready for review.
• Added backport release-x.y labels to auto-backport this PR, as appropriate.

How has this code been tested

$ go run ./cmd/up group list
NAME   PROTECTED

$ go run ./cmd/up group create nick-unprotected
nick-unprotected created
$ go run ./cmd/up group create nick-protected --deletion-protection
nick-protected created
$ go run ./cmd/up group list
NAME               PROTECTED
nick-protected     true
nick-unprotected   false

$ go run ./cmd/up group get nick-protected
NAME             PROTECTED
nick-protected   true

$ go run ./cmd/up group delete nick-protected
up: error: group.deleteCmd.Run(): Deletion protection is enabled on the specified group. Use '--force' to delete anyway.
exit status 1
$ go run ./cmd/up group delete nick-protected --force
nick-protected deleted
$ go run ./cmd/up group delete nick-unprotected
nick-unprotected deleted

[sttts]

is this one used?

I think we have to uniformely wire this through into GetCurrentContext(ctx).

[sttts]

Maybe also an idea, as we get more and more CRUD commands, we could create some common set of flags for CRUD.

[RedbackThomson]

Actually neither of these other CLI args are used - I was just looking over that myself. What is the purpose of this arg, anyway? Just another way to override the current context of the kubeconfig?

[sttts]

Yes, another way to override the kubeconfig/context.