fix: Update the link for Apache Gravtino

[shaofengshi]

Description

This PR includes the following changes:

1. The name "Apache Gravitino(incubating)" is inaccurate now, as the project has been graduated from Apache Incubator in June of 2026, so its formal name is "Apache Gravitino" now.
2. The code of Gravitino MCP server has been merged into its main repository, with a seperate folder;
3. Add a link to the documentation page on Gravitino asf web site.

(BTW, I'm one of the PMC member of Apache Gravitino project.)

Motivation and Context

Keep the information updated.

How Has This Been Tested?

We have integration test to ensure the functionality.

Breaking Changes

No

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Protocol Documentation
• My changes follows MCP security best practices
• I have updated the server's README accordingly
• I have tested this with an LLM client
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have documented all environment variables and configuration options

Additional context

No.