[CORL-3221] Part 1: Introduce full integration testing around auth and signup flows

[nick-funk]

What does this PR do?

• Introduces in-memory Redis and Mongo support for the testing environments
• Creates a bunch of mocks and helpers to support testing full request handlers
• Adds tests for the signup and auth flows (passport)
  • TODO: working on sso profiles tests now that signup flow has been mocked and tested

These changes will impact:

• commenters
• moderators
• admins
• developers

What changes to the GraphQL/Database Schema does this PR introduce?

None

Does this PR introduce any new environment variables or feature flags?

No

If any indexes were added, were they added to INDEXES.md?

No

How do I test this PR?

• Run the server tests

Were any tests migrated to React Testing Library?

No

How do we deploy this PR?

• Merge into develop

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