Improve CRD documentation (kubectl explain)

[weyfonk]

While Fleet CRDs are documented here, it is much more convenient to many users to be able to view information about a resource and its fields using kubectl explain.

We should ensure that the output of that command is as complete as possible for Fleet CRDs.
Some of the work is done, but some field types and resource descriptions are missing, eg:

$ kc explain bundle.spec
KIND:     Bundle                                                    
VERSION:  fleet.cattle.io/v1alpha1                                                                                                      
                                                                    
RESOURCE: spec <Object>                                             
                                                                    
DESCRIPTION:                                                                                                                            
     <empty>                                                        

FIELDS:                                                             
   correctDrift <Object>                                                                                                                
     CorrectDrift specifies how drift correction should work.

   defaultNamespace     <>                                          
     DefaultNamespace is the namespace to use for resources that do not specify
     a namespace. This field is not used to enforce or lock down the deployment
     to a specific namespace.                                       

   deleteCRDResources   <boolean>                                   
     DeleteCRDResources deletes CRDs. Warning! this will also delete all your
     Custom Resources.                                              

   deleteNamespace      <boolean>                                   
     DeleteNamespace can be used to delete the deployed namespace when removing
     the bundle                                                     

   dependsOn    <>                                                  
     DependsOn refers to the bundles which must be ready before this bundle can
     be deployed.                                                   
[...]

[manno]

Description for spec and status can be empty if the resource has a description.
For 0.10-rc I can also see types for all fields in bundle.

Please re-open if any public resources are missing descriptions for their fields.