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.

apps/web/package.json

@@ -14,6 +14,7 @@
     "copy:pdfjs": "node ../../scripts/copy-pdfjs.cjs"
   },
   "dependencies": {
+    "@documenso/api": "*",
     "@documenso/assets": "*",
     "@documenso/ee": "*",
     "@documenso/lib": "*",