v14: Add async methods to Deploy interfaces

[ronaldbarendse]

With most (if not all) services in v14 having async implementations (and new services even exclusively), this adds async methods to the Deploy interfaces, so we can implement 'async all the way'.

I've added these new async methods in a backwards-compatible way using default implementations that return Task.FromResult(...) and call the existing sync method. To signal to all callers and implementers to use the async methods, I've made the sync methods obsolete. This should allow us to first ensure the new async methods are implemented and called everywhere, remove the default implementations in the next major and finally remove the sync methods after being obsoleted for 2 major versions.