Binderhub: Rename the name of the `binder-` pod

[choldgraf]

One of the pods that BinderHub uses is just called binder-. This is a bit confusing, since all of the components _together_ make up binder. Perhaps we should choose a different name for the pod that's more explicit about what it does.

Also relates to #466

[yuvipanda]

We can call this binderhub-, should be a good first issue!

[mzc9]

Hi,

May I tackle this? Thanks

[yuvipanda]

@mzc9 yes please!