add solr-mcp-server to readme

[mjochum64]

Solr Search MR Description

Description

Adding a Solr search server implementation for MCP to enable efficient document search and retrieval capabilities within LLM workflows. This implementation allows models to search for documents in a Solr instance and retrieve relevant information based on queries.

Server Details

• Server: solr
• Changes to: tools, resources

Motivation and Context

This change adds Solr search capabilities to the MCP ecosystem, enabling LLMs to search and retrieve documents from Solr indexes. Solr offers powerful full-text search, faceting, and relevance scoring that can enhance LLM context retrieval. By integrating with Solr, the MCP protocol gains the ability to leverage mature enterprise search infrastructure that many organizations already have in place.

How Has This Been Tested?

• Tested with basic Solr search queries against a test instance
• Verified document retrieval functionality using pagination
• Tested various query parameters including filters and sorting
• Verified error handling for invalid queries and connection issues

Breaking Changes

No breaking changes to existing MCP client configurations. This adds a new server option without modifying existing functionality.

Types of changes

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• 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

The implementation supports configurable Solr instance URL, collection name, and search parameters. It handles authentication through environment variables for security. The server includes proper error handling for connection issues, invalid queries, and permission problems.