[CELEBORN-905] Redraw the flowchart backpressure.svg after worker pau…

…se logic is reconstructed

### What changes were proposed in this pull request?
Add a new `backpressure.svg` to replace the out-date one.

### Why are the changes needed?
After #1811, we refactor celeborn worker back-pressure logic, we should add new flowchart for user to understand.

### Does this PR introduce _any_ user-facing change?
Yes

### How was this patch tested?

![backpressure](https://github.com/apache/incubator-celeborn/assets/52876270/34f3f4b8-28cf-4cce-88a4-e6fee1886d94)

Closes #1829 from zwangsheng/CELEBORN-905.

Authored-by: zwangsheng <[email protected]>
Signed-off-by: zky.zhoukeyong <[email protected]>

common/src/main/scala/org/apache/celeborn/common/CelebornConf.scala

@@ -2474,7 +2474,7 @@ object CelebornConf extends Logging {
       .doc("If direct memory usage is less than this limit, worker will resume.")
       .version("0.2.0")
       .doubleConf
-      .createWithDefault(0.5)
+      .createWithDefault(0.7)
 
   val WORKER_CONGESTION_CONTROL_ENABLED: ConfigEntry[Boolean] =
     buildConf("celeborn.worker.congestionControl.enabled")