doc(v3): add first draft of migration guide with links to it

[scotthart]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @scotthart, 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 introduces the foundational V3 Migration Guide for the google-cloud-cpp SDK, aiming to streamline the transition for users upgrading to the v3.x.y release series. The guide addresses significant breaking changes, including updated C++ standard requirements, new Bazel integration methods, and modifications to project dependencies, providing a centralized resource to navigate these updates effectively.

Highlights

• New V3 Migration Guide: A new document, doc/v3-migration-guide.md, has been added to provide a comprehensive guide for users migrating from previous major versions (v1.x.y, v2.x.y) to the v3.x.y series of the google-cloud-cpp SDK.
• Documentation Links Added: Links to the newly created V3 Migration Guide have been prominently added to both CHANGELOG.md and README.md to ensure discoverability for users looking to update their applications.
• Migration Guide Content: The initial draft of the migration guide covers essential topics such as the requirement for C++17, integration with the Bazel Central Registry, changes to required dependencies (e.g., libcurl, nlohmann_json, opentelemetry-cpp), and outlines sections for decommissioned API surfaces across various components like Bigtable, Pubsub, and Spanner.

🧠 New Feature in Public Preview: You can now enable Memory to help Gemini Code Assist learn from your team's feedback. This makes future code reviews more consistent and personalized to your project's style. Click here to enable Memory in your admin console.

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 introduces a first draft of the v3 migration guide and adds links to it in CHANGELOG.md and README.md. The changes are a good starting point for documenting the migration process. My review includes a few suggestions to improve the consistency of links and formatting in the Markdown files to enhance readability.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.96%. Comparing base (febba47) to head (ef90e2c).
⚠️ Report is 2 commits behind head on prepare-for-v3.0.0.

Additional details and impacted files

@@                  Coverage Diff                   @@
##           prepare-for-v3.0.0   #15839      +/-   ##
======================================================
- Coverage               92.96%   92.96%   -0.01%     
======================================================
  Files                    2455     2455              
  Lines                  227501   227501              
======================================================
- Hits                   211495   211489       -6     
- Misses                  16006    16012       +6     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.