models: Add list archive lookup

models: Add list archive lookup

Add a list_archive_url_format field to Project, which will contain the
address of a Message-ID redirector, e.g. "https://lore.kernel.org/r/{}".

Add a list_archive_url property to Submission and Comment, to generate an
archive lookup URL based on the Message-ID.

We will use this to display links to mailing list archives.

Also add the new field to the default patchwork project fixture.

Suggested-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>