Run EXPLAIN with/without ANALYZE using a previously prepared statement

[vladich]

I haven't found a way to do this:

1. Using extended protocol, prepare a named statement (using v3 protocol feature, not the actual PREPARE statement), but do not actually run it
2. Instead, run EXPLAIN (ANALYZE) EXECUTE statement_name(....)
   Apparently this flow is not supported currently, but I would be happy to find if I'm wrong.
   If it's not supported, it would be great to support.