docs: Update trigger phrases and Jenkins job descriptions
docs: Update trigger phrases and Jenkins job descriptions

This commit adds a first, minimal description of the new
Cilium-PR-Ginkgo-Tests-Kernel Jenkins job and documents related, recent
changes to the trigger phrases.

Signed-off-by: Paul Chaignon <a027184a55211cd23e3f3094f1fdc728df5e0500@cilium.io>

cilium/cilium,tklauser/cilium,michi-covalent/cilium,tklauser/cilium,tgraf/cilium,cilium/cilium,tklauser/cilium,cilium-team/cilium,cilium/cilium,tklauser/cilium,tgraf/cilium,cilium/cilium,cilium-team/cilium,tgraf/cilium,michi-covalent/cilium,tgraf/cilium,michi-covalent/cilium,tgraf/cilium,michi-covalent/cilium,tklauser/cilium,michi-covalent/cilium,tgraf/cilium,cilium/cilium