Prepare release for opentelemetry-opamp-client v0.2b0 (#4381)

Co-authored-by: otelbot <197425009+otelbot@users.noreply.github.com>

Author: otelbot[bot]

opamp/opentelemetry-opamp-client/CHANGELOG.md

@@ -5,7 +5,7 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## Unreleased
+## Version 0.2b0 (2026-04-01)
 
 - Breaking change: callback class `Callbacks` renamed to `OpAMPCallbacks`
   ([#4355](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4355))

opamp/opentelemetry-opamp-client/src/opentelemetry/_opamp/version.py

@@ -12,4 +12,4 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-__version__ = "0.2b0.dev"
+__version__ = "0.2b0"