Temp-fix: Use isolatedModules in ts-jest

This will prevent a huge memory leak at the expense of type checking in
our tests. Once there is a better fix we should consider reverting this.

See: kulshekhar/ts-jest#1967
See: https://kulshekhar.github.io/ts-jest/user/config/isolatedModules

Author: daniel-ac-martin

jest.config.base.js

@@ -29,6 +29,7 @@ const config = {
   ],
   globals: {
     'ts-jest': {
+      isolatedModules: true,
       tsConfig: path.resolve(__dirname, 'tsconfig.nodejs.json')
     }
   }