feat: Add task_mode attr for aws_datasync_task

[acwwat]

Description

This PR is to add the recently released (enhanced) task mode feature to the aws_datasync_task resource. Note that enhanced task mode currently only supports transfer between S3 locations, and once set it cannot be changed (hence force new on this new argument).

Relations

Closes #39965

References

Referred to CreateTask for specs and wordings. Also referred to Choosing a task mode for your data transfer to confirm that task mode can only be set during task creation and not update.

Output from Acceptance Testing

$ make testacc TESTS="TestAccDataSyncTask_basic|TestAccDataSyncTask_taskMode" PKG=datasync
make: Verifying source code with gofmt...
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go1.23.2 test ./internal/service/datasync/... -v -count 1 -parallel 20 -run='TestAccDataSyncTask_basic|TestAccDataSyncTask_taskMode'  -timeout 360m
2024/10/31 22:09:26 Initializing Terraform AWS Provider...
=== RUN   TestAccDataSyncTask_basic
=== PAUSE TestAccDataSyncTask_basic
=== RUN   TestAccDataSyncTask_taskMode
=== PAUSE TestAccDataSyncTask_taskMode
=== CONT  TestAccDataSyncTask_basic
=== CONT  TestAccDataSyncTask_taskMode
--- PASS: TestAccDataSyncTask_taskMode (46.89s)
--- PASS: TestAccDataSyncTask_basic (171.48s)
PASS
ok      github.com/hashicorp/terraform-provider-aws/internal/service/datasync   171.704s

$

[github-actions]

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