### 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?
Closes#1829 from zwangsheng/CELEBORN-905.
Authored-by: zwangsheng <2213335496@qq.com>
Signed-off-by: zky.zhoukeyong <zky.zhoukeyong@alibaba-inc.com>
### What changes were proposed in this pull request?
As title.
### Why are the changes needed?
As title.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
Manual test.
Closes#1769 from waitinfuture/834.
Authored-by: zky.zhoukeyong <zky.zhoukeyong@alibaba-inc.com>
Signed-off-by: zky.zhoukeyong <zky.zhoukeyong@alibaba-inc.com>
### What changes were proposed in this pull request?
As title.
### Why are the changes needed?
As title.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
Manual test.
Closes#1754 from waitinfuture/831.
Authored-by: zky.zhoukeyong <zky.zhoukeyong@alibaba-inc.com>
Signed-off-by: zky.zhoukeyong <zky.zhoukeyong@alibaba-inc.com>
### What changes were proposed in this pull request?
As title.
### Why are the changes needed?
As title.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
No.
Closes#1752 from waitinfuture/826.
Authored-by: zky.zhoukeyong <zky.zhoukeyong@alibaba-inc.com>
Signed-off-by: zky.zhoukeyong <zky.zhoukeyong@alibaba-inc.com>
### What changes were proposed in this pull request?
As title.
### Why are the changes needed?
As title
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
No.
Closes#1747 from waitinfuture/824.
Authored-by: zky.zhoukeyong <zky.zhoukeyong@alibaba-inc.com>
Signed-off-by: zky.zhoukeyong <zky.zhoukeyong@alibaba-inc.com>
### What changes were proposed in this pull request?
As title.
### Why are the changes needed?
As title.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
No.
Closes#1746 from waitinfuture/823.
Authored-by: zky.zhoukeyong <zky.zhoukeyong@alibaba-inc.com>
Signed-off-by: zky.zhoukeyong <zky.zhoukeyong@alibaba-inc.com>
