feat: pico.config() now shows sources for provided parameters

Summary

• feat: picodata config default subcommand for generating a default config.yaml file

• feat: provide explicit defaults for log, vinyl & iproto config subsections

• feat: add parameter source "default" for pico.config() output

• feat: #[introspection(config_default = ".")] + Introspection::get_field_default_value_as_rmpv

• feat: pico.config() now shows sources for provided parameters

  Currently only 2 cases are supported:

  • config_file
  • commandline_or_environment

• feat: Introspection::set_field_from_rmpv

• feat: Introspection::FIELD_INFOS

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• Close #542 (closed)
• Target branch: master
• Changes should be cherry-picked to 24.2: no
• Docs follow-up: docs#243 (closed)
• Docs follow-up: docs#258 (closed)