Docs SEO improvements

[mortenpi]

Each page needs a separate and unique Title Tag. The pages below share title tags.

https://help.juliahub.com/julia-api/stable/guides/jobs/ Jobs · JuliaHub.jl
https://help.juliahub.com/julia-api/stable/reference/jobs/ Jobs · JuliaHub.jl

https://help.juliahub.com/julia-api/stable/reference/datasets/ Datasets · JuliaHub.jl
https://help.juliahub.com/julia-api/stable/guides/datasets/ Datasets · JuliaHub.jl

https://help.juliahub.com/julia-api/stable/guides/authentication/ Authentication · JuliaHub.jl
https://help.juliahub.com/julia-api/stable/reference/authentication/ Authentication · JuliaHub.jl

cc @mkstamand

[mortenpi]

I was hoping we could pages overrides for this (to still keep short titles in the navbar), but probably not. Instead, we probably need something like JuliaDocs/Documenter.jl#2155.