Update changelogs for v0.6.0 release (#38)

## Problem

The changelog and version number needs to be updated for Release v0.6.0.

## Solution

Updated the changelog and version number.

## Type of Change

- [ ] 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 not work as expected)
- [ ] This change requires a documentation update
- [ ] Infrastructure change (CI configs, etc)
- [X] Non-code change (docs, etc)
- [ ] None of the above: (explain here)

## Test Plan

NA

Author: rohanshah18

CHANGELOG.md

@@ -3,6 +3,10 @@
 [comment]: <> (When bumping [pc:VERSION_LATEST_RELEASE] create a new entry below)
 ### Unreleased version
 
+### v0.6.0
+- Add async stub for data plane operations
+- Add integration tests
+
 ### v0.5.1
 - Update build.gradle
 

build.gradle

@@ -9,7 +9,7 @@ plugins {
 }
 
 group = 'io.pinecone'
-version = '0.5.1' // [pc:VERSION_NEXT]
+version = '0.6.0' // [pc:VERSION_NEXT]
 description = 'The Pinecone.io Java Client'
 
 sourceCompatibility = JavaVersion.VERSION_1_8