Spike: Project-scoped export/import

[khvn26]

Currently, we allow environment-level import and export (default feature states only) accessible from UI, and CLI-based organisation-level import and export (projects, segments, features, environments and the segment/identity overrides).

We want to explore offering project-scoped exports that include segments and overrides, and allowing to create and import them via the UI.

The outcome of this spike should be an epic detailing out the implementation for the above.