Fix: Add Two-Dot Notation Support to pgagroal-cli conf get Command

[Userfrom1995]

Enhanced the pgagroal-cli conf get command to support two-dot notation (section.context.key) for precise configuration parameter retrieval, enabling commands like pgagroal-cli conf get limit.pgbench.max_size while maintaining backward compatibility with existing single-word queries.

[jesperpedersen]

@Userfrom1995 Please, do ports for pgmoneta and pgexporter as well