Make all necessary changes to support vcpkg dependents

[lugehorsam]

• Allows another repository to depend on this via vcpkg and sets this up as a vcpkg registry so we can push the decision to whether we want to add this to the vcpkg built-in registry to another time.

• Part of this was removing vcpkg as a subrepo, for a few reasons

  • I was noticing conflicts between the consumer's installation of vcpkg and the subrepo version. It's much easier to reason about a single vcpkg installation.
  • It didn't make sense to have manifests for every package (hundreds, thousands?) on vcpkg when we only use like five.

• Remove optional-lite from the CMake installation process. This was a wrong approach by me and is needed for vcpkg compatibility. Our any others trying to depend on ours via CMake should obtain optional-lite through their own means, e.g., a package manager like vcpkg.

• [x] Update test and examples to pull in optional-lite

• [ ] Document need to pull in optional-lite in README.md

[redbaron]

Just for the record, we had discussion about it and I was against this change for following reasons:

• there is no more <setup C++ toolchain> && git clone && cmake --build and dev need to follow setup instruction to make anything built
  • Also users now need to supply their own version of optional-lite to build , it is also not included in produced artifact and as a result our binary builds are not self-sufficient anymore
• vcpkg being on a side now builds will break in the future, because declared dependency versions will not be found anymore in future vcpkg trees. Builds are not reproducible.
• patches being moved to nakama-cpp-private makes nakama-cpp builds use different build (build flags, patches) of dependencies, meaning we introduce variability between platorms
• this change likely breaks XDK builds (educated guess, not verified), which now requires rewriting to be more like GDK (had to be done anyway, tbh)

[novabyte]

@redbaron What steps can be taken together to ensure that we can keep the two repositories broken apart as they need to be for legal reasons?

Let's figure out how to make it work and minimize the list of tradeoffs.