message: [telemetry] Track help topic
diff: #include <vcpkg/export.h>
  #include <vcpkg/help.h>
  #include <vcpkg/install.h>
  +#include <vcpkg/metrics.h>
  #include <vcpkg/remove.h>
  #include <vcpkg/vcpkgpaths.h>
  @@ -171,6 +172,7 @@ namespace vcpkg::Help
  if (topic == "triplets" || topic == "triple")
  {
  help_topic_valid_triplet(paths);
  + LockGuardPtr<Metrics>(g_metrics)->track_string_property(StringMetric::CommandContext, topic);
  Checks::exit_success(VCPKG_LINE_INFO);
  }
  @@ -178,11 +180,13 @@ namespace vcpkg::Help
  if (it_topic != topics.end())
  {
  it_topic->print(paths);
  + LockGuardPtr<Metrics>(g_metrics)->track_string_property(StringMetric::CommandContext, it_topic->name);
  Checks::exit_success(VCPKG_LINE_INFO);
  }
  msg::println_error(msgUnknownTopic, msg::value = topic);
  help_topics(paths);
  + LockGuardPtr<Metrics>(g_metrics)->track_string_property(StringMetric::CommandContext, "unknown");
  Checks::exit_fail(VCPKG_LINE_INFO);
  }
  