Remove references to implicit schema in Custom DC docs

[kmoscoe]

This is the second PR to remove all references to implicit schema. This PR updates the "prepare your data" and config file reference pages. A future PR will update the "custom entities" page.

Staged at bullie.svl.corp.google.com:4000

[gemini-code-assist]

Summary of Changes

Hello @kmoscoe, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly refines the Custom Data Commons documentation by removing all mentions and configurations related to the "implicit schema" approach. The changes consolidate the data import process into a single, explicit "variable-per-row" schema, simplifying the config.json file structure and streamlining the "prepare your data" guide. This effort aims to provide a clearer, more consistent, and less ambiguous experience for users preparing and loading custom data.

Highlights

• Unified Schema Approach: Eliminated all references to "implicit schema" in the documentation, standardizing on the "variable-per-row" (previously "explicit") schema for Custom Data Commons.
• Config.json Simplification: Removed configuration options and sections (variablePerColumn, ignoreColumns, idColumn, entityColumns, observationProperties, top-level entities and variables blocks) that were exclusively tied to the deprecated implicit schema.
• Streamlined Data Preparation Guide: Rewrote the "Prepare your data" guide to exclusively detail the single, now standard, data import method, including MCF definitions for statistical variables and the structure of CSV observation files.
• Documentation Clarity: Updated field descriptions and examples across config.md and custom_data.md to reflect the unified schema, removing confusing "implicit schema only" or "explicit schema only" qualifiers.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[gemini-code-assist]

Code Review

This pull request effectively removes references to the deprecated "implicit schema" from the Custom DC documentation, which simplifies the data preparation process for users. The changes correctly update the documentation to reflect that the variable-per-row format is now the standard. I've identified a couple of minor issues in the documentation: an incorrect reference and a grammatical error that should be addressed for clarity. Overall, this is a valuable cleanup.