Add patch to Snippet chooser to customize search

With this patch installed, the snippet chooser checks for a method
`chooser_search` in the model. If it exists, this method is used
instead of the search backend.

patches/Wagtail-Snippet-Chooser-Call-search-method-from-model-if-available.patch

@@ -0,0 +1,28 @@
+From 7b829bfdcd151a256788b99276db0566983b1ee6 Mon Sep 17 00:00:00 2001
+From: Donald Buczek <buczek@molgen.mpg.de>
+Date: Fri, 14 Aug 2020 22:55:59 +0200
+Subject: [PATCH] Chooser: Call search method from model if available
+
+---
+ .../site-packages/wagtail/snippets/views/chooser.py          | 5 ++++-
+ 1 file changed, 4 insertions(+), 1 deletion(-)
+
+diff --git a/lib/python3.7/site-packages/wagtail/snippets/views/chooser.py b/lib/python3.7/site-packages/wagtail/snippets/views/chooser.py
+index 7c93edd..26606cd 100644
+--- a/lib/python3.7/site-packages/wagtail/snippets/views/chooser.py
++++ b/lib/python3.7/site-packages/wagtail/snippets/views/chooser.py
+@@ -35,7 +35,10 @@ def choose(request, app_label, model_name):
+             search_query = search_form.cleaned_data['q']
+
+             search_backend = get_search_backend()
+-            items = search_backend.search(search_query, items)
++            if callable(getattr(model, "chooser_search", None)):
++                items = model.chooser_search(search_query)
++            else:
++                items = search_backend.search(search_query, items)
+             is_searching = True
+
+     else:
+-- 
+2.26.2
+