Auth failures on management endpoints such as team/list and
organization/list (invalid or expired keys) were raised as
ProxyException, whose __str__ returned an empty string, so the OTEL
SERVER span recorded an error with no message. ProxyException now
stringifies to its message, get_error_information prefers the explicit
.message attribute, and the proxy exception handlers stamp a consistent
error.type, error.code and error.message on the span
Resolves LIT-3515
f047b1571e