OFE: Add support for Shared VPCs.

[LasseHjorth]

This PR is a continuation of [#2597 2597] - but specific for OFE and this PR is also dependent of this.

The following changes explained:

• Allow Importing existing VPC to discover shared vpc and subnets.
• Fixed so page doesn't error out if there is no networks/subnets to import.
• Import existing VPC with full self_link names as cloud_ids.
• Moved network config to own blueprint jinja template.
• Removed private-service-access - this will break creating multiple clusters on the same VPC network, and belongs in community/front-end/ofe/infrastructure_files/vpc_tf/GCP.
• Modified create filestore filesystem to work with Shared VPCs. (connect mode).
• Fixed bug in create filestore filesystem, where ghpc was using machine identity and not the identity selected in frontend, to build TF code.
• Fixed bug in VPCDetailedView where any network would not be displayed if an ongoing cluster config is missing subnet.

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