Update release notes

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

RELEASE_NOTES.md

@@ -6,11 +6,20 @@
 
 ## Upgrading
 
-<!-- Here goes notes on how to upgrade from previous versions, including deprecations and what they should be replaced with -->
+- The old `frequenz.client.common.enum_proto` module is now deprecated, please use `frequenz.client.common.proto.enum_from_proto` instead.
 
 ## New Features
 
-<!-- Here goes the main new features and examples or instructions on how to use them -->
+- New `frequenz.client.common.common.proto` module with conversion utilities for protobuf types:
+  - `enum_from_proto()` (moved from `enum_proto).
+  - `datetime_to_proto()` and `datetime_from_proto()` functions to convert between Python `datetime` and protobuf `Timestamp` (imported from `frequenz-client-base`.
+- New `metrics` package compatible with API v0.8, which includes:
+  - `Metric` enum with all supported metrics.
+  - `MetricSample` dataclass to represent metric samples.
+  - `AggregatedMetricValue` dataclass to represent derived statistical summaries.
+  - `Bounds` dataclass to represent bounds for metrics.
+  - `MetricConnection` and `MetricConnectionCategory` to represent connections from which metrics are obtained.
+  - `proto` submodule with conversion functions to/from protobuf types.
 
 ## Bug Fixes