Consider design for CrdtMerge based on LfMerge

[rmunn]

We want to copy some of LfMerge's design (and, probably, code) to use in a CrdtMerge program, to mediate between Crdt projects and the Send/Receive system.

I'll record notes in this issue, which we will eventually turn into a design document.

[rmunn]

• Simple ASP.NET Core server
• Has its own k8s deployment
• Starts up and listens for requests to sync a project
• Will sync CRDT -> .fwdata or .fwdata -> CRDT
• Will then do a classic S/R to push a new commit to the Mercurial repo
• Will then call the CRDT API to push any new data from Mercurial back into the CRDT system