Create datagov-inventory repo #6355

Create a new Github repository for inventory 2.0. The repository should be named datagov-inventory, per standard Data.gov repo naming practice. It should follow all of the rules listed in https://github.com/GSA/data.gov/wiki/Checklist-for-new-repositories.

Reasons to build 2.0 in a new repo instead of in https://github.com/GSA/inventory-app/:

1. v1 and v2 will need to run concurrently for a period of time. Both codebases must be independently deployable and independently patchable during this time.
2. In switching from a CKAN-based app to a custom app, very little of the old codebase will be re-usable in the new app. A commit history that deletes most of the code and documentation before rebuilding is confusing, as is maintaining two long-lived branches that are vastly different.

There is precedent for creating a new repo since that is what the team did when they replaced the CKAN-based harvester and catalog apps.

Note that this task properly belongs to the design epic because we'd like to start storing architectural design documents in the new repo.