Improve the mechanism which Octopus uses for interacting with repositories in Config as Code Projects

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The current cloning mechanism used in CaC projects requires pulling down the entire repository. This can be less performant than ideal, particularly for cloud customers where this background process may happen any time an upgrade is pushed to a customer instance. In addition, some customers share their Octopus CaC configuration with their application code, which may result in many Gb of storage used just for us to access a few files.

Some experimentation suggests that interacting directly with the APIS of hosted git repository vendors may substantially improve this process, eliminating the time to clone (with some minimal tradeoff for accessing on demand) and eliminating the disk usage of cloned repositories.