boto: Apply patch needed to fix docker-registry

This makes docker-registry work when backed by S3. It's the same patch
applied in the docker upstream container image.

Backported from boto/boto#2932

pkgs/development/python-modules/boto/content-length-str.patch

@@ -0,0 +1,16 @@
+Cherry-picked from https://github.com/boto/boto/pull/2932
+
+This fix is required for things like docker-registry to interact with S3. Will
+be obsolete after the next boto release (> 2.36.0)
+
+--- a/boto/connection.py
++++ b/boto/connection.py
+@@ -381,7 +381,7 @@ class HTTPRequest(object):
+         if 'Content-Length' not in self.headers:
+             if 'Transfer-Encoding' not in self.headers or \
+                     self.headers['Transfer-Encoding'] != 'chunked':
+-                self.headers['Content-Length'] = len(self.body)
++                self.headers['Content-Length'] = str(len(self.body))
+
+
+ class HTTPResponse(http_client.HTTPResponse):

pkgs/top-level/python-packages.nix

@@ -1110,6 +1110,8 @@ let
     buildInputs = [ self.nose self.mock ];
     propagatedBuildInputs = [ self.requests self.httpretty ];
 
+    patches = [ ../development/python-modules/boto/content-length-str.patch ];
+
     meta = {
       homepage = https://github.com/boto/boto;