[TASK] Add TCA for new fields in member and membership

extensions/t3org_layout/Configuration/TCA/Overrides/tx_t3omembership_domain_model_member.php

+<?php
+
+$columns = [
+    'external_identifier' => [
+        'label' => 'External identifier (my.typo3.org)',
+        'exclude' => 1,
+        'config' => [
+            'type' => 'input',
+            'readOnly' => true,
+        ],
+    ],
+];
+
+\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addTCAcolumns(
+    'tx_t3omembership_domain_model_member',
+    $columns
+);
+\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addToAllTCAtypes(
+    'tx_t3omembership_domain_model_member',
+    'external_identifier',
+    '',
+    'after:hidden'
+);

extensions/t3org_layout/Configuration/TCA/Overrides/tx_t3omembership_domain_model_membership.php

+<?php
+
+$columns = [
+    'external_identifier' => [
+        'label' => 'External identifier (my.typo3.org)',
+        'exclude' => 1,
+        'config' => [
+            'type' => 'input',
+        ],
+    ],
+];
+
+\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addTCAcolumns(
+    'tx_t3omembership_domain_model_membership',
+    $columns
+);
+\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addToAllTCAtypes(
+    'tx_t3omembership_domain_model_membership',
+    'external_identifier',
+    '',
+    'after:hidden'
+);