Prepare for release version 0.8.1 (#445)

# Prepare for release version 0.8.1

Bump mcp kotlin-sdk to 0.8.1

## How Has This Been Tested?
Regression tests on CI

## Breaking Changes
<!-- Will users need to update their code or configurations? -->

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] 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)
- [x] Documentation update

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed

Author: kpavlov

gradle.properties

@@ -14,4 +14,4 @@ kotlin.mpp.enableCInteropCommonization=true
 kotlin.native.ignoreDisabledTargets=true
 
 group=io.modelcontextprotocol
-version=0.8.1-SNAPSHOT
+version=0.8.1