add access to server instructions

[jamesward]

Enable the MCP Client to read the Server instructions.

Motivation and Context

The instructions are optional and exist in the MCP spec, but not fully exposed in the Java SDK yet.

How Has This Been Tested?

Also made modifications to Spring AI and a test project that uses this.

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 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

[tzolov]

LGTM, thanks @jamesward