feat(gh-actions): gen2 e2e rest api

[Samaritan1011001]

Description of changes

Updates GH actions to take in additional backend parameter and call the sample staging app with it. Subsequent tests that need to be added for Gen2 only needs to add a new test case with the value backend: gen2 similar to what's shown here.

Issue #, if available

Description of how you validated changes

Passing GH actions on this branch.

Checklist

• [x] PR description included
• [x] yarn test passes
• [ ] Tests are changed or added
• [ ] Relevant documentation is changed or added (and PR referenced)

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