ha_connect.h max_supported_key_length arbitrarily too small

I'm currently working with the CONNECT storage engine connecting to a remote MySQL instance.

The max_supported_key_length value is hard-coded to only 255. This seems arbitrarily small, and increasing it in code and recompiling seem to =mostly= work.

The =mostly= part, max_supported_key_part_length is missing entirely from the CONNECT engine.

Both of these values are required for CONNECT federated INDEX hinting where the index length is larger than 255 bytes.

If both of these values can be set to a large value by default, that would be greatly appreciated, especially considering this note in the code:

// MySQL will do min(your_limits, MySQL_limits) automatically.

https://github.com/MariaDB/server/blob/10.11/storage/connect/ha_connect.h#L297

Additionally, it may be worth looking into the other "key" parameters too, such as max_supported_keys and max_supported_key_parts to ensure they're inline with other storage engines.