test: add tests for account linking example

[porcellus]

Summary of change

Note: this test will fail until we update try.supertokens.com with supertokens/supertokens-core#829

• added tests for account linking example
• updated the example for more consistent/easier testing

Related issues

Test Plan

N/A, example/test changes only

Documentation changes

N/A, example/test changes only

Checklist for important updates

• Changelog has been updated
• frontendDriverInterfaceSupported.json file has been updated (if needed)
• Changes to the version if needed
  • In package.json
  • In package-lock.json
  • In lib/ts/version.ts
• Had run npm run build-pretty
• Had installed and ran the pre-commit hook
• Issue this PR against the latest non released version branch.
  • To know which one it is, run find the latest released tag (git tag) in the format vX.Y.Z, and then find the latest branch (git branch --all) whose X.Y is greater than the latest released tag.
  • If no such branch exists, then create one from the latest released branch.
• If added a new recipe interface, then make sure that the implementation of it uses NON arrow functions only (like someFunc: function () {..}).
• If I added a new recipe, I also added the recipe entry point into the size-limit section of package.json with the size limit set to the current size rounded up.
• If I added a new recipe, I also added the recipe entry point into the rollup.config.mjs

[github-actions]

size-limit report 📦

Path	Size
lib/build/index.js	14.19 KB (0%)
recipe/session/index.js	15.15 KB (0%)
recipe/session/prebuiltui.js	17.77 KB (0%)
recipe/thirdpartyemailpassword/index.js	29.65 KB (0%)
recipe/thirdparty/index.js	26.43 KB (0%)
recipe/emailpassword/index.js	9.94 KB (0%)
recipe/emailverification/index.js	7.26 KB (0%)
recipe/passwordless/index.js	63.47 KB (0%)
recipe/thirdpartypasswordless/index.js	84.2 KB (0%)
recipe/emailverification/prebuiltui.js	22.46 KB (0%)
recipe/thirdpartyemailpassword/prebuiltui.js	53.8 KB (0%)
recipe/thirdparty/prebuiltui.js	38.51 KB (0%)
recipe/emailpassword/prebuiltui.js	27.52 KB (0%)
recipe/passwordless/prebuiltui.js	102.79 KB (0%)
recipe/thirdpartypasswordless/prebuiltui.js	130.42 KB (0%)
recipe/multitenancy/index.js	6.12 KB (0%)