Single-file API based project export/import facility (including LFS data)

Description

Provide a method to export/import all data associated with a project

Proposal

All should be placed within a single file (ex: .gz) such that it can be moved and then imported into another server. This file should contain LFS and other data that is be stored as part of the Git repo.

Export/import should be able to be initiated programmatically via an API call and/or rake task.

Ideally this would also work at the group level -- see also this issue: CE-13503

Links / references

Related issues:

Documentation blurb

TBD

/cc: @victorwu @pauldalmeida

Edited by Reb