reproducible VCR cassettes

[cfm]

Description

As of #1718, running make regenerate-sdk-cassettes does exactly that. But the result is basically unreviewable (e.g., 1f3c2c8). It would be nice to be able to set seed values for both the Server (Journalist API) and Client (SDK) sides of the SDK test suite, such make regenerate-sdk-cassettes could be diffed meaningfully.

@legoktm and I discussed this last night and I agreed that we'd like it. We didn't reach a conclusion on either (a) whether it's feasible or (b) whether it's worth doing.

How will this impact SecureDrop users?

No user-facing changes.

How would this affect the SecureDrop Workstation threat model?

No security implications.

User Stories

As developer going back and forth between the Server/API and Client/SDK, I would like to be able to use make regenerate-sdk-cassettes to diff the interaction between the two, not just blanketly commit the giant YAML blobs that come back.