docs: add detailed field descriptions to Config struct

[VolodymyrBg]

This commit adds comprehensive documentation for each field in the Config struct
in nodebuilder/config.go. The documentation helps users understand the purpose
and functionality of each configuration section, making it easier to configure
and maintain Celestia nodes.

Each field now includes a detailed comment that explains:

• What the configuration section controls
• Key functionality managed by that section
• Any node-type specific considerations (e.g., DASer for Light/Full nodes)

This addresses the TODO comment that requested field descriptions to help users
understand the purpose of each configuration field.

Resolves TODO(@Wondertan): Add field descriptions for Config struct