TM Provider Gateway

[Didainius]

This PR adds needed components for managing TM Provider Gateways:

• Added TmProviderGateway and types.TmProviderGateway structures and methods
  VCDClient.CreateTmProviderGateway, VCDClient.GetAllTmProviderGateways,
  VCDClient.GetTmProviderGatewayByName, VCDClient.GetTmProviderGatewayById,
  VCDClient.GetTmProviderGatewayByNameAndRegionId, TmProviderGateway.Update,
  TmProviderGateway.Delete to manage Provider Gateways
• Added TmTier0Gateway and types.TmTier0Gateway structures consumption and methods
  VCDClient.GetAllTmTier0GatewaysWithContext, VCDClient.GetTmTier0GatewayWithContextByName to
  read Tier 0 Gateways that are available for TM consumption
• Added TmIpSpaceAssociation and types.TmIpSpaceAssociation structures and methods
  VCDClient.CreateTmIpSpaceAssociation, VCDClient.GetAllTmIpSpaceAssociations,
  VCDClient.GetTmIpSpaceAssociationById,
  VCDClient.GetAllTmIpSpaceAssociationsByProviderGatewayId,
  VCDClient.GetAllTmIpSpaceAssociationsByIpSpaceId, TmIpSpaceAssociation.Delete to manage IP
  Space associations with Provider Gateways

Note. Testing of all these components is concentrated in Test_TmProviderGateway because everything is related and doesn't make much sense in isolation.

[lvirbalas]

Looks great!

[adambarreiro]

LGTM! Test passed