Add message representing electrical connections between components

This commit adds a new message `ComponentConnection` to represent
electrical connections between two components installed in a microgrid.
The message is not about data flow but rather about the physical
electrical connections between components. Therefore, the IDs for the
source and destination components correspond to the actual setup within
the microgrid.

Signed-off-by: Tiyash Basu <[email protected]>

Author: tiyash-basu-frequenz

RELEASE_NOTES.md

@@ -50,6 +50,9 @@
 - Added a message `ComponentCategoryMetadataVariant` to represent the different
   types of sub-categories that can be associated with a component category.
 
+- Added a message `ComponentConnection` to represent electrical connection
+  between two components installed in a microgrid.
+
 ## New Features
 
 <!-- Here goes the main new features and examples or instructions on how to use them -->

proto/frequenz/api/common/v1/components.proto

@@ -143,6 +143,43 @@ message Component {
   frequenz.api.common.v1.lifetime.Lifetime operational_lifetime = 9;
 }
 
+// ComponentConnection describes a single electrical link between two components
+// within a microgrid, effectively representing the physical wiring as viewed
+// from the grid connection point, if one exists, or from the islanding point,
+// in case of an islanded microgrids.
+//
+// !!! note "Physical Representation"
+//     This message is not about data flow but rather about the physical
+//     electrical connections between components. Therefore, the IDs for the
+//     source and destination components correspond to the actual setup within
+//     the microgrid.
+//
+// !!! note "Direction"
+//     The direction of the connection follows the flow of current away from the
+//     grid connection point, or in case of islands, away from the islanding
+//     point. This direction is aligned with positive current according to the
+//     [Passive Sign Convention]
+//     (https://en.wikipedia.org/wiki/Passive_sign_convention).
+//
+// !!! info "Historical Data"
+//     The timestamps of when a connection was created and terminated allows for
+//     tracking the changes over time to a microgrid, providing insights into
+//     when and how the microgrid infrastructure has been modified.
+//
+message ComponentConnection {
+  // Unique identifier of the component where the connection originates. This is
+  // aligned with the direction of current flow away from the grid connection
+  // point, or in case of islands, away from the islanding point.
+  uint64 source_component_id = 1;
+
+  // Unique ID of the component where the connection terminates. This is the
+  // component towards which the current flows.
+  uint64 destination_component_id = 2;
+
+  // The operational lifetime of the connection.
+  frequenz.api.common.v1.lifetime.Lifetime operational_lifetime = 3;
+}
+
 // ComponentData message aggregates multiple metrics, operational states, and
 // errors, related to a specific microgrid component.
 //