refactor: extract api implementation to package

Extracts the API implementation to a package so we can
potentially reuse it across different applications in the
event that we move off using a Next.js API route.

Additionally tidies up the tokens page and form to be more simplified.

packages/api/tsconfig.json

@@ -0,0 +1,8 @@
+{
+  "extends": "@documenso/tsconfig/react-library.json",
+  "include": ["."],
+  "exclude": ["dist", "build", "node_modules"],
+  "compilerOptions": {
+    "strict": true,
+  }
+}