Make account_id optional in mws_* resources

[alexott]

Changes

This change makes the account_id field optional for all MWS resources, allowing it to be specified either in the resource configuration or in the provider configuration block.

Resources updated:

• mws_customer_managed_keys
• mws_log_delivery
• mws_networks
• mws_private_access_settings
• mws_storage_configurations
• mws_vpc_endpoint
• mws_workspaces

Changes include:

• Updated struct field tags to make account_id optional and computed
• Added logic in Create functions to use provider's account_id when not specified in resource
• Added logic in Update functions (where applicable) to use provider's account_id
• Added comprehensive test coverage for each resource to ensure:
  • Resources can be created with account_id only in provider config
  • Resource IDs remain consistent regardless of where account_id is specified
  • Appropriate errors are returned when account_id is missing from both resource and provider

This change follows the same pattern as the mws_workspaces resource and ensures backward compatibility with existing configurations.

Tests

• make test run locally
• relevant change in docs/ folder
• covered with integration tests in internal/acceptance
• using Go SDK
• using TF Plugin Framework
• has entry in NEXT_CHANGELOG.md file

[github-actions]

If integration tests don't run automatically, an authorized user can run them manually by following the instructions below:

Trigger:
go/deco-tests-run/terraform

Inputs:

• PR number: 5133
• Commit SHA: a12b37acde43f9e15b9eade7e8f7ac950e2ee09e

Checks will be approved automatically on success.