add fixed_term_tenancy pattern to api docs and make it dynamically not required

app/models/case_log.rb

@@ -186,6 +186,10 @@ private
       dynamically_not_required << "net_income_frequency"
     end
 
+    if tenancy_type == "Fixed term – Secure"
+      dynamically_not_required << "fixed_term_tenancy"
+    end
+
     required.delete_if { |key, _value| dynamically_not_required.include?(key) }
   end
 end

docs/api/DLUHC-CORE-Data.v1.json

@@ -873,7 +873,8 @@
           },
           "fixed_term_tenancy": {
             "type": "string",
-            "minLength": 1
+            "minLength": 1,
+            "pattern": "((?!1|0)([0-9][0-9]))+"
           },
           "tenancy_type": {
             "type": "string",