Allow use of shared managed zones

[maleck13]

What

When setting up traffic controller, it should be possible to setup a default zone that is used by default for hosts in gateways etc.

Use Case
I don't want to have to setup a zone for every tenant ns but instead want to define a default zone that can be used by any tenant. Each tenant should receive a subdomain underneath the root domain of this zone

Option

Allow zones to be added to the same namespace as the traffic controller. By default these zones are considered shared. When a new namespace is added with a specific label, the controller should assign that new tenant a subdomain of the default zone. .

[maleck13]

@mikenairn added this after our conversation

[maleck13]

@mikenairn is this completed as part of the MZ PRs?

[mikenairn]

@maleck13 Yes i would say so. The controller looks for a MZ in the it's own NS, if none exists in the tenant NS.