This adds the ability to cache OpenWrt dependencies on a per-target
base. Artifacts over 10MB are excluded, as GitHub imposes a limit of 5G
of available space per repository cache. This affects mostly
linux(-firmware) and gcc / gdb.
The goal is to reduce the total amount of requests necessary to fetch
dependencies.
This adds a new workflow for building the Gluon documentation.
In contrast to the existing build workflow, the documentation
is built for every branch, as it only takes around two minutes
to render the HTML documentation.
