Update release notes

Signed-off-by: Leandro Lucarella <luca-frequenz@llucax.com>

Author: llucax

RELEASE_NOTES.md

@@ -6,14 +6,38 @@
 
 ## Upgrading
 
-<!-- Here goes notes on how to upgrade from previous versions, including deprecations and what they should be replaced with -->
+* The `UNSPECIFIED` members in the following enums are now deprecated:
+
+    * `frequenz.client.common.grid.EnergyMarketCodeType`
+    * `frequenz.client.common.metrics.Metric`
+    * `frequenz.client.common.metrics.MetricConnectionCategory`
+
+    When loading these types from protobuf using dataclass-level converters (e.g., `delivery_area_from_proto`, `metric_sample_from_proto`), the low-level fields (`code_type`, `category`, `metric`) now store the raw integer `0` for unspecified values instead of the deprecated member. Unspecified values should be rare errors, so it is better to expose them only via the low-level interface.
+
+    Lower-level enum-level converters still return the deprecated member.
+
+    Users are encouraged to switch from direct field access to the new `get_*()` methods (see New Features), which provide a safer way to handle unspecified or unrecognized values.
 
 ## New Features
 
+* Added new exceptions:
+
+    * `frequenz.client.common.ClientCommonError` as a base exception for the package.
+    * `frequenz.client.common.UnspecifiedValueError` for unspecified values (raw `0` or the deprecated member).
+    * `frequenz.client.common.UnrecognizedValueError` for enum members not yet recognized by the library. Carries the raw integer value in its `value` attribute.
+
+* Added safe convenience getters that raise the new exceptions for unspecified or unrecognized values:
+
+    * `frequenz.client.common.grid.DeliveryArea.get_code_type()`
+    * `frequenz.client.common.metrics.MetricConnection.get_category()`
+    * `frequenz.client.common.metrics.MetricSample.get_metric()`
+
 * Added a new `frequenz.client.common.types.Lifetime` type together with the `frequenz.client.common.types.proto.v1alpha8.lifetime_from_proto` conversion function.
+
 * Added a new `frequenz.client.common.types.Location` type together with the `frequenz.client.common.types.proto.v1alpha8.location_from_proto` conversion function.
+
 * Added a new `frequenz.client.common.microgrid.Microgrid` type, together with the `frequenz.client.common.microgrid.proto.v1alpha8.microgrid_from_proto` conversion function.
-* Added a new `frequenz.client.common.ClientCommonError` base exception and `UnspecifiedValueError` at the package root.
+
 * Added a new `frequenz.client.common.microgrid.electrical_components` package, featuring a `ElectricalComponent` class hierarchy and its families (battery, inverter, EV charger, etc.), and `ElectricalComponentConnection`, including `v1alpha8` proto conversion functions.
 * Added a new `frequenz.client.common.microgrid.Microgrid` type with a raising `is_active()` method, together with the `frequenz.client.common.microgrid.proto.v1alpha8.microgrid_from_proto` conversion function.