fix: added retry logic for reading resource subaccount entitlement

Purpose

Closes #902

Implemented the retry logic in the Read function of the resource subaccount entitlement to overcome the rate limiting issue faced. This is accomplished by placing the GET call within a loop, enabling the function to manage rate limiting errors accordingly.

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:

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

SAP / terraform-provider-btp

fix: added retry logic for reading resource subaccount entitlement #910