feat(check_approval): add support for pre and post approval kinds

[Luiz Felipe Machado (luizfelmach)]

All Submissions:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My code follows the code style of this project.
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Description

Adds support for selecting the approval check kind in azuredevops_check_approval.
Azure DevOps uses different settings.definitionRef.id values for standard approvals, pre-check approvals, and post-check approvals, but the provider previously only modeled a generic approval check. This change adds a new optional approval_kind attribute so users can explicitly manage these variants through Terraform.
Supported values:

• approval
• pre_check
• post_check
  This change also updates the flatten/expand logic to map approval_kind to the correct settings.definitionRef.id, updates the resource documentation, and adds test coverage for the new behavior.

Does this introduce a breaking change?

• Yes
• No

Test Result

$ go test -tags=all ./azuredevops/internal/service/approvalsandchecks -run 'TestCheckApproval_|TestApprovalKindDefinitionRefMapping'
ok  	github.com/microsoft/terraform-provider-azuredevops/azuredevops/internal/service/approvalsandchecks	0.003s
$ go test ./azuredevops/internal/acceptancetests -run '^TestDoesNotExist$'
ok  	github.com/microsoft/terraform-provider-azuredevops/azuredevops/internal/acceptancetests	0.005s
Related Issue(s)
Fix #0000
Other information
Azure DevOps distinguishes approval kinds using these definitionRef.id values:
- approval: 26014962-64a0-49f4-885b-4b874119a5cc
- pre_check: 0f52a19b-c67e-468f-b8eb-0ae83b532c99
- post_check: 06441319-13fb-4756-b198-c2da116894a4

[William (williamoconnorme)]

Closes #1586