Json enum extensions

[CJ-SPT]

This is a two part PR that must be merged with the modules PR of the same name.

The goal of this PR is to provide an easier way to extend enums than having to write their own pre-patchers and understanding the pitfalls that come with using libs like Mono.Cecil or AsmResolver.

• Removes the ability to use raw pre-patchers on the server. It's unnecessary for the server, we have full control of this code. An Enum extension abstraction through Json is enough.
• Implements Json based Enum extensions for the server, using a Json file that replaces the former prepatcher dll in the same location keyed by mod guid.
• Implements the required backend code for the new pre-patchers http request
• Server Enum extensions are loaded directly by the server at start due to needing them early
• Client Enum extensions must be loaded and added to the injected singleton ClientEnumDefinitions manually by mod authors. This singleton only exists if the mod loader is enabled.

[ArchangelWTF]

LGTM, the migration docs on the wiki will need updating