fix: Improved Error Handling for Entitlement Destruction

[ANUGRAHG]

Purpose

This PR resolves issue #837
The issue at hand highlights the lack of a relevant error message when attempting to destroy entitlements under specific conditions. One such scenario arises when trying to destroy an entitlement for which a service instance exists outside of Terraform's lifecycle.

To address this, an update has been made to the Delete() function of the resourceSubaccountEntitlement. This update allows the error message to be propagated from the AssignedServicePlanSubaccountDto response object, providing more informative feedback during the destruction process.

Does this introduce a breaking change?

[ ] Yes
[x] No

Pull Request Type

What kind of change does this Pull Request introduce?

[x] Bugfix
[ ] Feature
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:

How to Test

• Test the code via automated test

go test ./...

What to Check

Verify that the following are valid:

• Automated tests are executed successfully

Checklist for reviewer

The following organizational tasks must be completed before merging this PR:

• The PR is assigned to the Terraform project and a status is set (typically "in review").
• The PR has the matching labels assigned to it.
• The PR has a milestone assigned to it.
• If the PR closes an issue, the issue is referenced.
• Possible follow-up items are created and linked.

[lechnerc77]

lgtm