Make config list output more user-friendly

[dbarnett]

Now that there's a basic jj config list command, we want to improve it to give more user-friendly output:

• Hide implicit defaults and only show explicit config values (with --include-defaults option to override)
• Instead of just sorting alphabetically, order output more logically to correspond to the config layers and their contents
• Support --repo, --user, and other target specifiers #2827
• Support --include-overridden argument to config list command. #2828
• Colorize output
• Add a --show-sources option to report where each config value came from (similar to git's --show-origin and hg's --debug)