[PM-6165] Add x-enum-varnames to improve swagger generation (#3767)

Improves code generation of enums for the server bindings in the sdk. Bindings will now use the appropiate variable name from the server.

Works by adding a filter which appends x-enum-varnames to enums with the name from c#.

src/SharedWeb/Swagger/EnumSchemaFilter.cs

@@ -0,0 +1,26 @@
+using Microsoft.OpenApi.Any;
+using Microsoft.OpenApi.Models;
+using Swashbuckle.AspNetCore.SwaggerGen;
+
+namespace Bit.SharedWeb.Swagger;
+
+/// <summary>
+/// Adds x-enum-varnames containing the name of enums. Useful for code generation.
+///</summary>
+/// <remarks>
+/// Ideally we would use `oneOf` instead but it's not currently handled well by our swagger generator.
+///
+/// Credits: https://github.com/domaindrivendev/Swashbuckle.WebApi/issues/1287#issuecomment-655164215
+/// </remarks>
+public class EnumSchemaFilter : ISchemaFilter
+{
+    public void Apply(OpenApiSchema schema, SchemaFilterContext context)
+    {
+        if (context.Type.IsEnum)
+        {
+            var array = new OpenApiArray();
+            array.AddRange(Enum.GetNames(context.Type).Select(n => new OpenApiString(n)));
+            schema.Extensions.Add("x-enum-varnames", array);
+        }
+    }
+}