feat(secure): add sysdig_secure_zone_posture_policy_assignment resource

[tembleking]

New resource sysdig_secure_zone_posture_policy_assignment that manages the association between a sysdig_secure_zone and a set of posture policy IDs via the CSPM API (/api/cspm/v1/zones/{zoneId}/policies).

This is a standalone resource (not embedded in sysdig_secure_zone) because the APIs have different lifecycles and it allows assigning policies to system zones the user didn't create. The resource ID is the zone ID (1:1 relationship), and zone_id is ForceNew since changing it means a different resource.

Depends on backend routing enablement: draios/sysdigcloud-harness-cd#75479

Ref: ET-836

[Copilot]

Pull request overview

Adds a new Terraform resource to manage CSPM posture-policy assignments for Secure Zones via the /api/cspm/v1/zones/{zoneId}/policies API, enabling policy management for both user-created and system zones as a standalone lifecycle.

Changes:

• Introduces sysdig_secure_zone_posture_policy_assignment resource with CRUD + import (resource ID = zone ID).
• Adds a v2 client implementation (ZonePolicyAssignmentInterface) and models for the new CSPM endpoint.
• Adds acceptance coverage and provider registration, plus new user documentation for the resource.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
website/docs/r/secure_zone_posture_policy_assignment.md	New documentation page for the resource, including example usage and import.
sysdig/resource_sysdig_secure_zone_posture_policy_assignment.go	Implements the Terraform resource schema and CRUD operations.
sysdig/resource_sysdig_secure_zone_posture_policy_assignment_test.go	Adds acceptance test coverage for create/update/import flows.
sysdig/provider.go	Registers the new resource in the provider.
sysdig/internal/client/v2/zone_policy_assignment.go	Adds v2 API client methods for zone policy assignments.
sysdig/internal/client/v2/model.go	Adds request/response structs for the new endpoint.
sysdig/internal/client/v2/client.go	Extends SecureCommon to include the new interface.
sysdig/common.go	Adds a shared SchemaZoneIDKey constant used by the new resource.

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