Instrument Repository Idea (Like Ubuntu PPA)

[joshunrau]

Previously, the plan was to move as many instruments as possible into this repo. However, there are a lot of licensing issues (including with GPL) related to that.

Since we are going to have to have at least some instruments elsewhere anyways, why not host all instruments in a separate repo (related to #976). This repo will be publicly available and be the base repository available in any ODC instance. Admins can add additional Git repositories to their instance. which are assumed to follow a set structure (we could create a template repo). That way, people can add their own, private repositories, for restricted instruments.

Admins can add instruments from these repositories to their instance, as needed.