chore: update Gitleaks ignore for MESH polling documentation

Add Gitleaks ignore entry for false positive generic-api-key detection
in MESH polling README documentation

Author: josielsouzanordcloud

.gitleaksignore

@@ -25,3 +25,4 @@ manage_breast_screening/config/settings_test.py:private-key:34
 manage_breast_screening/config/settings_test.py:public-key:61
 manage_breast_screening/config/.env.tpl:generic-api-key:36
 manage_breast_screening/config/.env.tpl:generic-api-key:42
+manage_breast_screening/notifications/management/commands/README_MESH_POLLING.md:generic-api-key:207