Catch-all variants for more janus_messages enums

[divergentdave]

Currently we have catch-all enum variants for HPKE algorithm identifiers, to enable graceful handling of unsupported keys. We should add similar variants to other enums where it makes sense, so we can finish decoding messages where possible, and then return more tailored error messages from application logic, instead of urn:ietf:params:ppm:dap:error:invalidMessage. Note that this will be a breaking change to janus_messages.