Compute: Add support for FLEX_START and RESERVATION_BOUND provisioning model

[MihajloLinic]

compute: added `FLEX_START` and `RESERVATION_BOUND` support to `google_compute_instance`, `google_compute_instance_template`, and `google_compute_region_instance_template`

Fixed version of PR: #16750
Error was during testing not accounting for recording mode

This PR adds support for the FLEX_START and RESERVATION_BOUND provisioning models to google_compute_instance, google_compute_instance_template, and google_compute_region_instance_template.

FLEX_START is a VM scheduling option in Google Cloud Compute Engine (part of the Dynamic Workload Scheduler) that allows flexible start times for VM instances, enabling cost optimization by letting Google schedule VM creation within a 24-hour time window. It is specifically designed for accelerator-optimized workloads (GPUs/TPUs).

RESERVATION_BOUND is a VM scheduling option that binds an instance to a specific reservation. When set, the instance will only consume capacity from the targeted reservation (configured via reservation_affinity). This is used with Calendar Reservations (Future Reservations) in the Dynamic Workload Scheduler, where GPU/TPU capacity is pre-booked for a specific time window and delivered as a standard reservation that instances can then target.

Changes

• Schema Updates: Added FLEX_START and RESERVATION_BOUND as valid values for provisioning_model in the scheduling block of instances and instance templates. Updated field descriptions and validation logic.
• TGC Support: Updated Terraform Google Conversion (TGC) logic to ensure FLEX_START and RESERVATION_BOUND are correctly handled during resource conversion.
• Documentation: Updated the resource and data source documentation for instances and templates to include FLEX_START (with its required companion fields like instance_termination_action and max_run_duration) and RESERVATION_BOUND (with its companion reservation_affinity block).
• Tests: Added comprehensive acceptance tests for both provisioning models across all affected resources:
  • TestAccComputeInstance_flexStart, TestAccComputeInstanceTemplate_flexStart, TestAccComputeRegionInstanceTemplate_flexStart
  • TestAccComputeInstance_reservationBound, TestAccComputeInstanceTemplate_reservationBound, TestAccComputeRegionInstanceTemplate_reservationBound

[github-actions]

Googlers: For automatic test runs see go/terraform-auto-test-runs.

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[slevenick]

We can't move a field from output-only to required without a breaking change. Why is this becoming required now?

[MihajloLinic]

In google cloud API future reservations are zone based, for endpoint you need to sent which zone you are consuming reservation from. Variables that construct the url have to be under parameters: . if zone was left where it was users wouldn't be able to provide it in their .tf config

[github-actions]

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