feature: add hostname to the gw login page and sidebar

[g6094199]

i use several chirpstack installations on different locations. sometimes its had to recognize the gw you are working on right now. they all look the same!

so it would be nice to have the hostname (maybe the ip, too) display on the loginpage:

and the left sidebar:

and no the tab dispalys the name but is most of the time nor readable:

thx
sash