add support for proxy base path routing

[csantanapr]

add support for proxy base path routing when using vscode-server port-forward proxy

Motivation and Context

When running mcpinspector from inside vscode-server and in a vm and not localhost route path is required for both the client UI (6274) and the mcp-proxy (6277)
For example I'm using aws cloudfront in front of ec2 running vscode-server, and when running npx @modelcontextprotocol/inspector the server is available in a url like this https://d2udq1bmhskoal.cloudfront.net/proxy/6274

How Has This Been Tested?

I tested this on aws with cloudfront/ec2, mcp server running on ec2 locahost as streameable http on port 8000
Here is a screenshot

Breaking Changes

No braking changes

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 Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context