Collect credentials from the end user when creating a new survey

[zimeg]

Type of change

• New sample
• New feature
• Bug fix
• Documentation

Summary

This PR changes the credential_source from DEVELOPER to END_USER to perform actions – such as creating a new spreadsheet – as the individual invoking the "Create a survey" workflow instead of from the shared developer token.

This removes the need to filter triggers by a list of approved surveyors, which makes this sample a bit more simple!

Todo

Before reviews or merging, the following tasks remain:

• Update the demo videos in the README.md

Requirements

• I’ve checked my submission against the Samples Checklist to ensure it complies with all standards
• I have ensured the changes I am contributing align with existing patterns and have tested and linted my code
• I've read and agree to the Code of Conduct

[zimeg]

• Update the demo videos in the README.md

Quick note: Another change will soon follow that updates the survey/response flow – planning to add an ephemeral message after a response is submitted! Updating the first demo is left for this following PR.