Report statistics about oximeter collections

- Some oximeter collector crate reorg and cleanup
- Add target representing an oximeter collector service itself
- Add metrics representing the number of successful collections, and
  number of failed collections broken out by a few reasons

oximeter/collector/Cargo.toml

@@ -8,6 +8,7 @@ license = "MPL-2.0"
 [dependencies]
 anyhow.workspace = true
 camino.workspace = true
+chrono.workspace = true
 clap.workspace = true
 dropshot.workspace = true
 futures.workspace = true
@@ -26,6 +27,7 @@ slog.workspace = true
 slog-async.workspace = true
 slog-dtrace.workspace = true
 slog-term.workspace = true
+strum.workspace = true
 thiserror.workspace = true
 tokio.workspace = true
 toml.workspace = true