refac(opensearch): Use new WaitHelper for waiters

[Fyusel]

STACKITSDK-385

Description

Checklist

• Issue was linked above
• No generated code was adjusted manually (check comments in file header)
• Changelogs
  • Changelog in the root directory was adjusted (see here)
  • Changelog(s) of the service(s) were adjusted (see e.g. here)
• VERSION file(s) of the service(s) were adjusted
• Code format was applied: make fmt
• Examples were added / adjusted (see examples/ directory)
• Unit tests got implemented or updated
• Unit tests are passing: make test (will be checked by CI)
• No linter issues: make lint (will be checked by CI)

[rubenhoenle]

Could be half the code 😉

// note the private visibility for the shared logic
func createOrUpdateInstanceWaitHandler(ctx context.Context, a opensearch.DefaultAPI, projectId, instanceId string) *wait.AsyncActionHandler[opensearch.Instance] {
	waitConfig := wait.WaiterHelper[opensearch.Instance, string]{
		FetchInstance: a.GetInstance(ctx, projectId, instanceId).Execute,
		GetState: func(s *opensearch.Instance) (string, error) {
			if s == nil {
				return "", errors.New("empty response")
			}
			if s.Status == nil {
				return "", errors.New("status is missing")
			}
			return *s.Status, nil
		},
		ActiveState: []string{INSTANCESTATUS_ACTIVE},
		ErrorState:  []string{INSTANCESTATUS_FAILED},
	}

	handler := wait.New(waitConfig.Wait())
	handler.SetTimeout(45 * time.Minute)
	return handler
}

func CreateInstanceWaitHandler(ctx context.Context, a opensearch.DefaultAPI, projectId, instanceId string) *wait.AsyncActionHandler[opensearch.Instance] {
    return createOrUpdateInstanceWaitHandler(...)
}

func PartialUpdateInstanceWaitHandler(ctx context.Context, a opensearch.DefaultAPI, projectId, instanceId string) *wait.AsyncActionHandler[opensearch.Instance] {
    return createOrUpdateInstanceWaitHandler(...)
}

You can then also use the test construct I've shown @GokceGK here to test all 3 implementations using the same logic:

#7163 (comment)