[Proposal] SOAR-0012 Generate enums for server variables (#629)

### Motivation

As requested by @czechboy0 in #618 I have created this proposal for
community feedback.

### Modifications

Added the proposal.

Also fixed a typo in the document for the proposal process.

### Result

N/A

### Test Plan

N/A

---------

Co-authored-by: Honza Dvorsky <honza@apple.com>

Author: theoriginalbit

Sources/swift-openapi-generator/Documentation.docc/Proposals/Proposals.md

@@ -4,7 +4,7 @@ Collaborate on API changes to Swift OpenAPI Generator by writing a proposal.
 
 ## Overview
 
-For non-trivial changes that affect the public API, the Swift OpenAPI Generator project adopts a ligthweight version of the [Swift Evolution](https://github.com/apple/swift-evolution/blob/main/process.md) process.
+For non-trivial changes that affect the public API, the Swift OpenAPI Generator project adopts a lightweight version of the [Swift Evolution](https://github.com/apple/swift-evolution/blob/main/process.md) process.
 
 Writing a proposal first helps discuss multiple possible solutions early, apply useful feedback from other contributors, and avoid reimplementing the same feature multiple times.
 
@@ -52,3 +52,4 @@ If you have any questions, tag [Honza Dvorsky](https://github.com/czechboy0) or
 - <doc:SOAR-0008>
 - <doc:SOAR-0009>
 - <doc:SOAR-0010>
+- <doc:SOAR-0012>