feat: Typescript for API layer (#817)

Co-authored-by: Philip Korsholm <88927411+pKorsholm@users.noreply.github.com>
Co-authored-by: Zakaria El Asri <33696020+zakariaelas@users.noreply.github.com>
Co-authored-by: Kasper Fabricius Kristensen <45367945+kasperkristensen@users.noreply.github.com>
Co-authored-by: Philip Korsholm <philip.korsholm@hotmail.com>
Co-authored-by: Sebastian Rindom <seb@medusa-commerce.com>

packages/medusa-js/jestconfig.json

@@ -0,0 +1,7 @@
+{
+  "transform": {
+    "^.+\\.(t|j)sx?$": "ts-jest"
+  },
+  "testRegex": "(/tests/.*|(\\.|/)(test|spec))\\.(jsx?|tsx?)$",
+  "moduleFileExtensions": ["ts", "tsx", "js", "jsx", "json", "node"]
+}