Support go-import meta tags
Summary:
GoGetMetaRepositoryExtension is a class which adds custom handling
of diffusion requests that include ?go-get=1 in the url.
To make this work, a custom extension mechanism was added to
DiffusionRepositoryController in D775
Test Plan:
see test plan in D775
Depends-on: D775
Reviewers: dduvall
Differential Revision: https://phabricator.wikimedia.org/D776