Include inventory file for interlinking docs

[sethaxen]

From v1.3.0, Documenter has included an objects.inv inventory file in the built docs, which packages to use DocumenterInterLinks.jl to link to documentation of methods/objects in other packages. This works fine for Documenter-built packages, but DocumenterVitepress does not seem to include an inventory file. It would be great if this package could include this file.