fix: add additionalproperties to the sdkContextSchema (#4682)

This was changed a month ago, but it ends up breaking the frontend when
we regenerate the types because the playground needs to have this
structure for now. We'll need to add this back until we can rewrite the
playground to follow the schema.

src/lib/openapi/spec/sdk-context-schema.ts

@@ -5,6 +5,7 @@ export const sdkContextSchema = {
     description: 'The Unleash context as modeled in client SDKs',
     type: 'object',
     required: ['appName'],
+    additionalProperties: true,
     properties: {
         appName: {
             type: 'string',