fix: Update changelog with migration guide for form field value consumption

Summary of change

This PR updates the changelog to add details of the form field type change

(If relevant, please create a PR in our docs repo, or create a checklist here highlighting the necessary changes)

[x] Changelog has been updated
[ ] coreDriverInterfaceSupported.json file has been updated (if needed)
- Along with the associated array in supertokens_python/constants.py
[ ] frontendDriverInterfaceSupported.json file has been updated (if needed)
[ ] Changes to the version if needed
- In setup.py
- In supertokens_python/constants.py
[x] Had installed and ran the pre-commit hook
[x] 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 have added a new web framework, update the supertokens_python/utils.py file to include that in the FRAMEWORKS variable
[ ] If added a new recipe that has a User type with extra info, then be sure to change the User type in supertokens_python/types.py
[ ] Make sure that syncio / asyncio functions are consistent.
[ ] If access token structure has changed
- Modified test in tests/sessions/test_access_token_version.py to account for any new claims that are optional or omitted by the core