Add configuration-based tasks to the guides

[jmacdotorg]

After the configuration reference gets published (#374), we should follow up with updates to the guide about how to accomplish various discrete tasks that have to do with setting CodeRabbit's behavior in specific behavior.

For example: add an “Adjust review behavior by path” section to the “Review pull requests” guide pages, and explain how to define path instructions.

This project involves, as a first step, some planning of what the user journeys to document even are.

[linear]

ENG-1568 Add configuration-based tasks to the guides

[traycerai]

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