Optimize post method of the Settings class

[kwajiehao]

Currently, we make multiple API calls to update the various settings files (_config.yml, _data/navigation.yml, _data/footer.yml) even if no changes have been made to some of those files. Since, we are unable to make concurrent POST calls to GitHub, this results in the saving process for the Settings layout on the frontend to be very slow (currently it takes more than 7 seconds).

For example, if we receive a payload where only the title field has been modified, we should only update the _config.yml file. This would let our code run faster since we don't have to wait for the outcome of the other two meaningless API calls.

Resolving this issue might involve changing frontend code, since currently the frontend sends the data for all the fields that are displayed on the Settings layout. We need to modify the frontend to only send modified data, not all data present on the page.