Add duckdb.temp_directory and duckdb.max_temp_directory_size

[TianzeMYou]

I see duckdb has a temp_directory setting and uses it when the memory limit is exhausted. Though i don't see this setting for pg_duckdb, could we add this GUC? 

see https://duckdb.org/docs/stable/configuration/overview.html#:~:text=v0.10.2-,temp_directory,-Set%20the%20directory

[TianzeMYou]

Could we expose a setting for extension directory location?
https://duckdb.org/docs/stable/configuration/overview#:~:text=VARCHAR-,extension_directory,-Set%20the%20directory

[Y--]

Great points, thanks for the suggestions. Addressed in #699

[JelteF]

Fixed now by #704