Port EquinoxWeb template to C#

[bartelink]

This PR is in service of the following missions:

• Polish Equinox's surface APIs, removing pain points accessing from C# and validating aspects of the F# usage:
  • its not a big conceptual stretch to support it, especially given recent language additions in v6 and 7 wrt pattern matching and expression bodies members etc
  • little effort has been invested in basics such making Equinox be natural for use from languages other than F# to date
• Providing another way to illustrate the concepts of idempotent command processing, events, folds etc which are commonly agreed
• provide a base sample that others can use refactor from to illustrate other (read: better) approaches using alternate libraries and techniques
• improve the F# implementation via the above cross-polination (doing this exercise has highlighted numerous bugs/oversimplifications in the F#)

HT @aarondandy who put in lots of legwork to motivate the work (and various other discussions on the DDD-CQRS-ES Slack)

Components:

• port wiring for Cosmos, EventStore and MemoryStore in aspnetcore
  • I'm not entirely happy with some of the compromises in how I separate the code vs what works well with DUs in F# and am definitely open to PRs to make things better
  • By the same token, I'm not entirely dissatisfied - its important that the wiring be close to idiomatic C# and not too slavish a translation of what happens to work well in F#
• Provide basic shims allowing Handler functions to be written without F# interop (FuncConvert etc) littering the place (open to PRs to do more, but for now the key synchronous one is ported and life will go on)
• port Aggregate.fs to C#
• port Todo.fs to C#
• Port TodosController.fs to C#
• make it compile
• make sure it actually runs and functions correctly per https://todobackend.com (shouldn't be hard as it this is just a port, but its absolutely not been run)
• include equinox-web-csharp as a component within the Equinox.Templates nuget (consumption experience should only differ in having to specify a -l C#, i.e. it should go in sharing the same identity as the F# one)
• make improvements to Equinox (e.g. defaults etc) to enable simplification of some of the wiring (for now the plan is that C# wiring will continue to live in Infrastructure.cs, but if any tweaks and/overloads are needed in the Equinox repo, that'll be done - i.e. this may be experimental, but C# support is intended to be a first class supported thing) - see Tweaks for C# interop equinox#81 - this will merge after final integration test against 1.0.3-rc1 packages
• Final test required of 1.1.0-rc3 per readme in this branch
• Merge the key cleanup aspects of Experiment: Polish eqxweb C# template by using OneOf library to pattern match #6 in here (but probably not the OneOf ref)

Future work:

• Perhaps provide an example of defining the Event and/or Command DUs in F# in order to attempt to see whether that's a better approach that the Encode/TryDecode implementation that's presently in place (I really believe its worth doing this work, even if the likelihood of one doing that for any sustained period is not the most likely)