feat: remove MyInfo error_description support

[mantariksh]

Problem

When the MyInfo consent flow returns an error, we support both error-description (note hyphen) and error_description (note underscore) in the query parameters. This is because we were previously unsure which one would be returned - the documentation says that it should be error_description, but the sandbox and staging APIs both returned error-description. Now that we have confirmed that production returns error-description as well, we can drop support for error_description.

Part of #1234

Solution

Drop support for error_description. For safety, in case MyInfo decides to add other query parameters, also add unknown(true) to the Joi validation.

Mockpass previously returned error_description, but since this PR which went into v2.6.5, it now returns error-description, so I upgraded Mockpass to make the dev environment match production.

Tests

• Log in to a MyInfo form but click "Cancel" on the consent page. Ensure that you see the MyInfo error when redirected back to the form, and that there is matching message in the logs (message: 'MyInfo returned error from consent flow') which contains an errorDescription.

[liangyuanruo]

Remove .unknown(true) before merge? It's good as long as the parameters we're using are validated.