feat(stresstest): Add batch mode using many API

stresstest/config/example.yaml

@@ -1,30 +1,15 @@
-remote: http://localhost:18888
+remote: http://localhost:8888
 
-duration: 5s
+duration: 10s
 
 workloads:
-  - name: attachments
-    mode: throughput
-    organizations: 1000
+  - name: snapshots
+    mode: batch
+    concurrency: 1
     file_sizes:
-      p50: 50 KiB
-      p99: 200 KiB
+      p50: 5 KiB
+      p99: 20 KiB
     actions:
-      writes: 10
+      writes: 20000
       reads: 0
       deletes: 0
-  - name: profiling
-    concurrency: 8
-    file_sizes:
-      p50: 15 KiB
-      p99: 100 KiB
-  - name: replays
-    concurrency: 16
-    file_sizes:
-      p50: 25 KiB
-      p99: 400 KiB
-  - name: nodestore
-    concurrency: 32
-    file_sizes:
-      p50: 5 KiB
-      p99: 20 KiB

stresstest/src/http.rs

@@ -84,7 +84,7 @@ impl HttpRemote {
         Ok(())
     }
 
-    fn session(&self, usecase: &Usecase, organization_id: u64) -> Session {
+    pub(crate) fn session(&self, usecase: &Usecase, organization_id: u64) -> Session {
         // NB: Reuse the organization ID as project ID to create unique projects. Right now, we do
         // not benefit from simulating multiple projects per org.
         usecase