doc: document how to use custom TLS certificates for Hubble
doc: document how to use custom TLS certificates for Hubble

In addition, remove beta warning now that mTLS is supported by Hubble
and enabled by default.

Signed-off-by: Robin Hahling <042b6757f29293f4affc22596084b908e3917891@gw-computing.net>

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