Support uploading host_name info in the tool event logger

host_name info is useful in several use cases including
1) to distinguish the concurrent tool invocations from the same user.
2) to understand the potential different performance from different hosts (e.g. local workstation VS cloudtop).
3) required to integrate the tool event log with the EPR system.

Test: atest tool_event_logger_test
Bug: 348482213

Change-Id: I98422b3f8ccec73d57fcdcdedac91780c448dc47

tools/tool_event_logger/proto/tool_event.proto

@@ -27,6 +27,8 @@ message ToolEvent {
   string source_root = 3;
   // Name of the tool used.
   string tool_tag = 6;
+  // Name of the host workstation.
+  string host_name = 7;
 
   oneof event {
     InvocationStarted invocation_started = 4;