api: support filtering patches by hash

api: support filtering patches by hash

This is a feature that the XML-RPC API has, and which is used in
the wild [1], so support it in the REST API.

I tried to version the new filter field, but it's not at all clear
how to do this with django-filters. The best way I could find
requires manually manipulating request.GET, which seems to defeat
the point of django-filters. So document it for 1.2, and have it
work on older versions as an undocumented feature.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/mricon/korg-helpers.git/tree/git-patchwork-bot.py?id=104e7374e1be8458e6d2e82478625a7bf8c822ff

Cc: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
Signed-off-by: Daniel Axtens <dja@axtens.net>
Acked-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>