Add Jenkins builder with --enable-tor2web-mode

We could easily break tor2web compilation, and never know it. So let's add a Jenkils builder on Debian with ./configure --enable-tor2web-mode

Unit tests currently fail to launch in tor2web mode, so we won't be able to enable them (or we'll need to mask failures) until #20061 (moved) is fixed.

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