[56] Implement shared session between Rails <=> Phoenix

[cpreisinger]

Description

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Related Issues

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Changes Made

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Checklist

• [ ] PR is assigned to a project: Challenge_gov Board
• [ ] PR is assigned to a milestone: current sprint
• [ ] GH issues are assigned to the PR (under Development section on the right hand side)
• [ ] PR is assigned a reviewer, and requires code review and approval by a teammate
• [ ] New functionality is tested and all tests are green
• [ ] I have added unit tests for new functionality or updated existing tests for changes.
• [ ] I have updated the documentation/README accordingly, if necessary.
• [ ] If you have DB migration, it is a "safe" migration and you've confirmed it can be rolled back.
• [ ] If applicable, Controllers modified contain appropriate authorization plugs
• [ ] This PR has been reviewed by at least one other team member.