Deploy sites to pages with gRPC API calls

It's an architectural problem for us that in order to deploy a site to gitlab-pages, gitlab-rails (sidekiq) needs to write the update to disk behind gitlab-pages's back (see gitlab-com/migration#31 (closed)). The biggest problem this causes for us at the moment is that it forces us to use some sort of shared file system (NFS in our current gitlab.com infrastructure); this is problematic when we move to Kubernetes.

One thing we could do about this is to create an admin HTTP gRPC API inside pages for site deploys, and instead of having gitlab-rails write sites to disk, have it send them to this admin API inside pages.

Customers

https://gitlab.my.salesforce.com/0016100001EogBS
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