Listen for /v3 on CSAPI (#2197)
Listen for /v3 on CSAPI (#2197)

* Listen for /v3 on CSAPI

* Docs

* More docs

* Rename path variable to fix key backup tests

* Update routing.go

Co-authored-by: Neil Alexander <7f0e7998f0d3082a84355a2366a12924c14a9eda@users.noreply.github.com>
matrix-org/dendrite,matrix-org/dendrite,matrix-org/dendrite,matrix-org/dendrite