✨ v1beta2: Standardize flavor in OpenStackMachine

[nikParasyr]

/kind feature

As part of the v1beta2 api improvements:

OSM: Update flavor to follow id/filter standard:

Current the OSM allows the following:

Kind: OpenStackMachine
...
spec:
  ...
  flavor: <Name of flavor>
  flavorID: <ID of flavor>
  ...

This should be updated to the one below so that its consistent with all other fields:

Kind: OpenStackMachine
...
spec:
  ...
  flavor:
    ID: <ID of flavor>
    Filter:
      Name: ...
      <other list options of flavor>
  ...

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

[nikParasyr]

/assign