Read all cgroup v2 metrics that can be read (#1120)

### What does this PR do?

This commit removes any arbitration of the cgroup v2 heirarchy for a
given process. We instead read anything that can be read, looping over
all cgroup files present but not following the hierarchy down.

Metric names will change but they will now reflect underlying system reality.

Author: blt

Cargo.lock

@@ -1,5 +1,2 @@
 generator: []
-
-blackhole:
-  - tcp:
-      binding_addr: "0.0.0.0:8080"
+blackhole: []

examples/lading-idle.yaml

@@ -87,7 +87,6 @@ quanta = { version = "0.12", default-features = false, features = [] }
 zstd = "0.13.1"
 
 [target.'cfg(target_os = "linux")'.dependencies]
-cgroups-rs = { version = "0.3", default-features = false, features = [] }
 procfs = { version = "0.17", default-features = false, features = [] }
 async-pidfd = "0.1"
 

lading/Cargo.toml

@@ -112,7 +112,10 @@ impl Server {
         let target_pid = target_pid.expect("observer cannot be used in no-target mode");
 
         let mut sample_delay = tokio::time::interval(Duration::from_secs(1));
-        let mut sampler = Sampler::new(target_pid)?;
+        let mut sampler = Sampler::new(
+            target_pid,
+            vec![(String::from("focus"), String::from("target"))],
+        )?;
 
         let shutdown_wait = self.shutdown.recv();
         tokio::pin!(shutdown_wait);