Fix terminology in the ListConnections RPC

[llucax]

What's needed?

The ListConnections RPC has a request message that talks about start and end, which is a bit confusing, as it sounds like it might be referring to ranges of IDs, which is very weird.

frequenz-api-microgrid/proto/frequenz/api/microgrid/v1/microgrid.proto

Lines 360 to 370 in 8f4e4f8

	// Request parameters for the RPC `ListConnections`.
	// Contains filtering parameters for listing connections.
	message ListConnectionsRequest {
	// Only return connections that start from the specified component ID(s):
	// if empty, connections with any `start` will be returned
	repeated uint64 starts = 1;
	// Only return connections that end at the specified component ID(s):
	// if empty, connections with any `end` will be returned
	repeated uint64 ends = 2;
	}

The ComponentConnection message in api-common was renamed to use source and destination instead of start and end, so the microgrid API should probably adopt those terms too.

Proposed solution

// Request parameters for the RPC `ListConnections`.
// Contains filtering parameters for listing connections.
message ListConnectionsRequest {
  // Only return connections that originate from the specified component ID(s):
  // if empty, connections with any `source_component_id` will be returned
  repeated uint64 source_component_ids = 1;

  // Only return connections that terminate at the specified component ID(s):
  // if empty, connections with any `destination_component_id` will be returned
  repeated uint64 destination_component_ids = 2;
}

Use cases

No response

Alternatives and workarounds

No response

Additional context

No response