Ignore X.509 users in scram secret collision validation (#123)

# Summary
During validation, users without the scramCredentialsSecretName
parameter are
[added](https://github.com/mongodb/mongodb-kubernetes/blob/7fa6687dd12bc523f6d5df834672c849b1b737ed/mongodb-community-operator/controllers/validation/validation.go#L95)
to a dictionary with an empty key, which leads to the error mentioned in
issue #122.

Closes #122

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---------

Signed-off-by: Vadim Aleksandrov <[email protected]>

Author: verdel

mongodb-community-operator/controllers/validation/validation.go

@@ -85,14 +85,16 @@ func validateUsers(mdb mdbv1.MongoDBCommunity) error {
 
 		// Ensure no collisions in the secret holding scram credentials
 		scramSecretName := user.ScramCredentialsSecretName
-		if previousUser, exists := scramSecretNameMap[scramSecretName]; exists {
-			scramSecretNameCollisions = append(scramSecretNameCollisions,
-				fmt.Sprintf(`[scram secret name: "%s" for user: "%s" and user: "%s"]`,
-					scramSecretName,
-					previousUser.Username,
-					user.Username))
-		} else {
-			scramSecretNameMap[scramSecretName] = user
+		if scramSecretName != "" {
+			if previousUser, exists := scramSecretNameMap[scramSecretName]; exists {
+				scramSecretNameCollisions = append(scramSecretNameCollisions,
+					fmt.Sprintf(`[scram secret name: "%s" for user: "%s" and user: "%s"]`,
+						scramSecretName,
+						previousUser.Username,
+						user.Username))
+			} else {
+				scramSecretNameMap[scramSecretName] = user
+			}
 		}
 
 		if user.Database == constants.ExternalDB {