cypto.getPrivate(): fix error when passphrase kinda works

[alxndrsn]

Closes #1212

Sometimes an incorrect passphrase can still "successfully" decrypt supplied the supplied ciphertext, but to nonsense. In this case, the call to createPrivateKey() will throw an error that was not previously handled by the surrounding try/catch block.

What has been done to verify that this works as intended?

Added tests.

Why is this the best possible solution? Were any other approaches considered?

The full error generated can be:

Error: error:1E08010C:DECODER routines::unsupported
    at createPrivateKey (node:internal/crypto/keys:726:12)
    at /home/user/workspaces/odk/backend/lib/util/crypto.js:164:14 {
  opensslErrorStack: [ 'error:1E08010C:DECODER routines::unsupported' ],
  library: 'DECODER routines',
  reason: 'unsupported',
  code: 'ERR_OSSL_UNSUPPORTED'
}

Checking error.code seems like it should be reasonably stable.

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

Should reduce 500 errors or similar.

Does this change require updates to the API documentation? If so, please update docs/api.yaml as part of this PR.

Hopefully not.

Before submitting this PR, please make sure you have:

• run make test and confirmed all checks still pass OR confirm CircleCI build passes
• verified that any code from external sources are properly credited in comments or that everything is internally sourced

[matthew-white]

Looks great, it sounds like this is getting to the root cause of the issue.

[matthew-white]

I'm going to take this PR out of the project, since the associated issue is also in the project.