crimson: fix stack-use-after-return in ConfigProxy::parse_argv

ConfigProxy::parse_argv used to take std::vector<const char*>& and capture
it by reference in a lambda passed to do_change(), which invokes the lambda
on another shard via invoke_on. By the time the target shard ran the lambda,
the caller had returned and the referenced vector was destroyed.

Fix: take std::vector<std::string> by value and move it into the closure,
so the data outlives the call. Convert to vector<const char*> only on the
target shard, and return the unrecognized leftover args so callers still
see which flags were consumed by md_config_t::parse_argv().

Signed-off-by: Alexander Indenbaum <aindenba@redhat.com>
Co-authored-by: Cursor <cursoragent@cursor.com>