Replace http routing library & update endpoints to match

CHANGELOG.md

api/_apimeta/auth.go

api/_auth_cache/auth_cache.go

api/_responses/content.go

api/_responses/errors.go

api/_responses/meta.go

api/_routers/00-install-params.go

api/_routers/01-install_metadata.go

api/_routers/02-install-headers.go

api/_routers/03-host_detection.go

api/_routers/04-request-metrics.go

api/_routers/97-optional-access-token.go

api/_routers/97-require-access-token.go

api/_routers/97-require-repo-admin.go

api/_routers/98-use-rcontext.go

api/_routers/99-response-metrics.go

api/auth.go

api/custom/datastores.go

api/custom/exports.go

api/custom/federation.go