Add GitKraken MCP server

[cmgriffing-at-gitkraken]

MCP Server Information

Server Name: GitKraken
Repository URL: https://github.com/gitkraken/mcp
Brief Description: Work with Git repositories, issues, and pull requests through GitKraken.

Basic Requirements

• Open Source: Uses acceptable license (Apache-2.0, MIT, BSD-2-Clause, BSD-3-Clause or other permissive license)
• MCP Compliant: Implements MCP API specification
• Active Development: Recent commits and maintained
• Docker Artifact: Dockerfile
• Documentation: Basic README and setup instructions
• Security Contact: Method for reporting security issues

Submitter Checklist

• This server meets the basic requirements listed above
• I understand this will undergo automated and manual review.
• I have tested the MCP Server using task validate -- --name gitkraken
• I have built the MCP Server using task build -- --tools gitkraken
• If the server requires credentials to test it, I have shared test credentials using this form (Not applicable; image build and tool discovery are auth-independent.)