Publish dockerbuilder images for Jessie too

Hello!

Please add Jessie images at https://salsa.debian.org/salsa-ci-team/images/tree/master/dockerfiles in addition to the existing Unstable and Stretch ones. Some of us are still shipping security updates etc to old-stable and would need to test stuff on Jessie.

Thanks!

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information