Export-DbaCredential - Add IF NOT EXISTS guard to exported SQL scripts

Wraps each CREATE CREDENTIAL statement with an IF NOT EXISTS check against
sys.credentials so that exported scripts are idempotent and only create
missing credentials during migrations or DR script replays.

Closes #8618

(do Export-DbaCredential)

Co-authored-by: Andreas Jordan <andreasjordan@users.noreply.github.com>

Author: github-actions[bot]

public/Export-DbaCredential.ps1

@@ -165,14 +165,15 @@ function Export-DbaCredential {
 
             foreach ($cred in $credentials) {
                 $quotename = $cred.Quotename
+                $credName = $cred.Name.Replace("'", "''")
                 $identity = $cred.Identity.Replace("'", "''")
                 $password = $cred.Password.Replace("'", "''")
                 $cryptoSql = ""
                 if ($cred.MappedClassType -like 'Cryptographic*') {
                     $providerName = $cred.ProviderName
                     $cryptoSql = " FOR CRYPTOGRAPHIC PROVIDER $providerName"
                 }
-                $sql += "CREATE CREDENTIAL $quotename WITH IDENTITY = N'$identity', SECRET = N'$password'" + $cryptoSql
+                $sql += "IF NOT EXISTS (SELECT 1 FROM sys.credentials WHERE name = N'$credName') CREATE CREDENTIAL $quotename WITH IDENTITY = N'$identity', SECRET = N'$password'" + $cryptoSql
             }
 
             if ($Passthru) {

tests/Export-DbaCredential.Tests.ps1

@@ -108,6 +108,10 @@ Describe $CommandName -Tag IntegrationTests {
         It "Should have the password" {
             $exportResults | Should -Match "ReallyT3rrible!"
         }
+
+        It "Should include IF NOT EXISTS guard" {
+            $exportResults | Should -Match "IF NOT EXISTS"
+        }
     }
 
     Context "Should export a specific credential" {