Add a chapter on the long filter for magento plugin (#65)

* Add a chapter on the long filter for magento plugin

* Improve description, add some fancy things

Author: JoMessina

content/connectivity/magento-2/_index.en.md

@@ -137,6 +137,37 @@ In this example we will search for customers that were updated after 1985 (`@dat
 # ...
 ```
 
+#### With long filter
+Filters are passed to the url.
+But the most popular web browsers will not work with URLs over 2000 characters, and would return a 414 (Request-URI Too Long).
+You can use the method `withLongFilter` to avoid this limitation and batch your request in multiple smaller requests.
+
+In this example we will search for specific orders with a lot of elements in the request's filter.
+We have 214 increment_id, and we use a `withLongFilter` with parameters: 
+ - `@order_increment_id` references our order's filter.
+ - `offset`, starts the request at the chosen index, by default we have 0.
+ - `length`, defines a batch length, by default we have 200.
+
+Here we have set an offset to 0 and a length to 150, it means we are starting the request from the first element and make multiple requests with 150 items max.
+```yaml
+# ...
+      order_filter_group:
+        class: Kiboko\Component\Flow\Magento2\FilterGroup
+        calls:
+          - withLongFilter: [ '@order_filter' ]
+      order_filter:
+      class: Kiboko\Component\Flow\Magento2\FilterGroup
+      calls:
+        - withLongFilter: ['@order_increment_id', 0, 150]
+      order_increment_id:
+        class: Kiboko\Component\Flow\Magento2\Filter
+        arguments:
+          - 'increment_id'
+          - 'in'
+          - '000000526,4000000026,00000918,000001754,6000000123,4000000150,6000000185,000003798,6000000211,[..],5000000445'
+# ...
+```
+
 ### Building a lookup
 There is a lookup class for Categories, and one for product Attributes.