✨ v1beta2: Add managedRouters on OpenStackCluster

[nikParasyr]

/kind feature

As part of the v1beta2 api improvements:

Group router related fields under managedRouter

For most of the resources that capo creates we have a field with managedXYZ. This is not the case for router, so:

Kind: OpenStackCluster
...
spec:
  ...
  externalRouterIPs:
  - fixedIP: XYZ
    subnet:
      filter:
        name: ZYX
  ...

Should be grouped into:

Kind: OpenStackCluster
...
spec:
  ...
  managedRouter:
    externalIPs:
    - fixedIP: XYZ
      subnet:
        filter:
          name: ZYX
  ...

Implementation should be done after core v1beta2 is implemented in #2895

[nikParasyr]

/assign