Add DataPipe file saving example to survey docs/examples

[becky-gilbert]

The new survey plugin has a "file" question type for requesting file uploads from the participant. This question type requires the user to handle the file somehow. One option is to store the file as Base64-encoded text in the jsPsych data, but this is not ideal for large files. We should add an example of how to handle a file upload with DataPipe.

For reference when creating this example:
Example code and docs: https://surveyjs.io/form-library/examples/file-upload/jquery#
File question API docs: https://surveyjs.io/form-library/documentation/api-reference/file-model

While we're at it, we could add similar DataPipe examples for other plugins/extensions that can generate a lot of data:

• html-audio-response
• sketchpad
• record-video