Add TimeIntervalFilter definition (#313)

Refs frequenz-floss/frequenz-api-dispatch#243
Refs frequenz-floss/frequenz-api-dispatch#242
Refs
frequenz-floss/frequenz-api-electricity-trading#142

Author: Marenz

RELEASE_NOTES.md

@@ -18,6 +18,7 @@
 - Added new message `SensorDiagnostic` to represent warnings and errors in microgrid sensors.
 - The enum `SensorErrorCode` has now been renamed to `SensorDiagnosticCode` to better reflect its shared usage with warnings and errors.
 - Added warnings to sensor `SensorState`.
+- Added a common `TimeIntervalFilter` message in `frequenz.api.common.v1.types` to standardize time interval filtering across APIs. This uses `start_time` (inclusive) and `end_time` (exclusive) fields, aligning with ISO 8601 and common programming conventions.
 
 ## Bug Fixes
 

proto/frequenz/api/common/v1/types/time_interval_filter.proto

@@ -0,0 +1,35 @@
+// A time interval filter.
+//
+// Copyright 2025 Frequenz Energy-as-a-Service GmbH
+//
+// Licensed under the MIT License (the "License");
+// you may not use this file except in compliance with the License.
+
+syntax = "proto3";
+
+package frequenz.api.common.v1.types;
+
+import "google/protobuf/timestamp.proto";
+
+
+// Represents a time interval filter.
+//
+// The interval includes the start time and excludes the end time.
+// This follows the convention used in ISO 8601 for time intervals,
+// Pandas slicing, and Python slicing: [start_time, end_time).
+//
+// * If `start_time` is omitted, the interval is
+//   considered unbounded at the start.
+// * If `end_time` is omitted, the interval is
+//   considered unbounded at the end.
+message TimeIntervalFilter {
+  // The beginning of the time interval (inclusive).
+  //
+  // Must be a UTC timestamp.
+  google.protobuf.Timestamp start_time = 1;
+
+  // The end of the time interval (exclusive).
+  //
+  // Must be a UTC timestamp.
+  google.protobuf.Timestamp end_time = 2;
+}