What changes were proposed in this pull request?

This PR introduces a new CHANGELOG.md file to provide a centralized and structured history of Apache Gravitino releases following the Keep a Changelog format.

Additionally, the README.md has been updated with a Changelog section that links users directly to the changelog and the project's GitHub Releases page, making release information easier to discover.

Why are the changes needed?

Currently, the repository does not provide a dedicated changelog document that summarizes release history in a single location. Adding a CHANGELOG.md improves documentation by:

• Providing a clear overview of notable changes across releases.
• Making it easier for users to track new features, bug fixes, and improvements.
• Following a widely adopted changelog format for better readability and maintenance.
• Improving discoverability by linking the changelog from the project's README.

Fix: N/A

Does this PR introduce any user-facing change?

Yes.

• Adds a new CHANGELOG.md file containing the project's release history.
• Updates the README.md to include a link to the changelog and GitHub Releases.
• No APIs, configurations, or runtime behavior are changed.

How was this patch tested?

• Verified that CHANGELOG.md is rendered correctly on GitHub.
• Verified that the links in README.md correctly navigate to CHANGELOG.md and the GitHub Releases page.
• Confirmed that the documentation changes do not affect the project's build or functionality.