config: replace fse read functions with sync variants

I need to be able to read the config at module load time, which makes
async difficult if not impossible.

This will make read config operations synchronous, which is fine. The
file is tiny and seldom read.

app/server/lib/config.ts

@@ -2,9 +2,9 @@ import * as fse from "fs-extra";
 
 // Export dependencies for stubbing in tests.
 export const Deps = {
-  readFile: fse.readFile,
+  readFile: fse.readFileSync,
   writeFile: fse.writeFile,
-  pathExists: fse.pathExists,
+  pathExists: fse.pathExistsSync,
 };
 
 /**