fix(proxy): fix proxy header construction for two_step (#3314)

## Describe the problem and your solution
Fix Proxy header construction for `two_step` auth mode.

<!-- Issue ticket number and link (if applicable) -->

<!-- Testing instructions (skip if just adding/editing providers) -->

---------

Co-authored-by: Hassan Wari <hassanwari@Hassans-MacBook-Pro.local>

packages/shared/lib/services/proxy.service.ts

@@ -76,52 +76,39 @@ class ProxyService {
         let token;
         switch (connection.credentials.type) {
             case 'OAUTH2':
-                {
-                    const credentials = connection.credentials;
-                    token = credentials.access_token;
-                }
+            case 'APP': {
+                const credentials = connection.credentials;
+                token = credentials.access_token;
                 break;
-            case 'OAUTH1': {
-                const error = new Error('OAuth1 is not supported yet in the proxy.');
-                const nangoError = new NangoError('pass_through_error', error);
-                return { success: false, error: nangoError, response: null, logs };
             }
-            case 'BASIC':
-                token = connection.credentials;
-                break;
-            case 'API_KEY':
-                token = connection.credentials;
-                break;
-            case 'APP':
-                {
-                    const credentials = connection.credentials;
-                    token = credentials.access_token;
-                }
-                break;
             case 'OAUTH2_CC':
-                {
-                    const credentials = connection.credentials;
-                    token = credentials.token;
-                }
-                break;
+            case 'TWO_STEP':
             case 'TABLEAU':
-                {
-                    const credentials = connection.credentials;
-                    token = credentials.token;
-                }
-                break;
             case 'JWT':
-                {
-                    const credentials = connection.credentials;
-                    token = credentials.token;
-                }
+            case 'SIGNATURE': {
+                const credentials = connection.credentials;
+                token = credentials.token;
                 break;
-            case 'SIGNATURE':
-                {
-                    const credentials = connection.credentials;
-                    token = credentials.token;
-                }
+            }
+            case 'BASIC':
+            case 'API_KEY':
+                token = connection.credentials;
                 break;
+            case 'OAUTH1': {
+                const error = new Error('OAuth1 is not supported yet in the proxy.');
+                const nangoError = new NangoError('pass_through_error', error);
+                return { success: false, error: nangoError, response: null, logs };
+            }
+            case 'APP_STORE':
+            case 'CUSTOM':
+            case 'TBA':
+            case undefined:
+            case 'BILL': {
+                break;
+            }
+            default: {
+                throw new Error(`Unhandled connection.credentials for: ${(connection.credentials as any).type}`);
+            }
         }
 
         const provider = getProvider(providerName);
@@ -470,6 +457,7 @@ class ProxyService {
                         case 'API_KEY':
                         case 'OAUTH2_CC':
                         case 'TABLEAU':
+                        case 'TWO_STEP':
                         case 'JWT':
                             if (value.includes('connectionConfig')) {
                                 value = value.replace(/connectionConfig\./g, '');