Terraform support for best path selection

[modular-magician]

Modified the following beta fields in google_compute_network Gateway resource (b/343562168)

• gateway_ip_version (enum): Added new enum field "bgp_best_path_selection_mode" with possible values Legacy and Standard
• bgp_bps_always_compare_med (bool): Added new bool field
• gateway_ip_version (bgp_bps_inter_region_cost): Added new enum field "bgp_bps_inter_region_cost" with possible values Default and Add-cost-to-med

3 new beta output fields for google_compute_router_status for best_routes & best_routes_for_router fields

• gateway_ip_version (enum): Added new enum field "bgp_best_path_selection_mode" with possible values Legacy and Standard
• route.next_hop_origin
• route.next_hop_med
• route.next_hop_inter_region_cost
  Release Note Template for Downstream PRs (will be copied)

compute: added `bgp_best_path_selection_mode `,`bgp_bps_always_compare_med` and `bgp_bps_inter_region_cost ` fields to `google_compute_network` resource

compute: added `next_hop_origin `,`next_hop_med ` and `next_hop_inter_region_cost ` output fields to `google_compute_route` resource

Derived from GoogleCloudPlatform/magic-modules#11825

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