Use button array for survey

The buttons will be now be contained in an array instead of having hard coded accept and reject texts at the top level

Each button will also have the ability to link to a url specified within the object

Pre-launch Checklist

[x] I read the Contributor Guide and followed the process outlined there for submitting PRs.
[x] I read the Tree Hygiene wiki page, which explains my responsibilities.
[x] I read the Flutter Style Guide recently, and have followed its advice.
[x] I signed the CLA.
[x] I listed at least one issue that this PR fixes in the description above.
[x] I updated/added relevant documentation (doc comments with ///).
[x] I added new tests to check the change I am making, or this PR is test-exempt.
[x] All existing and new tests are passing.

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