Lightning: split backoff is not long enough, and fail when EBS BR disabled region split

[mittalrishabh]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. Run EBS BR while lightning is running. It might fail lightning if BR suspends region split for more than 1 - 2 min.

2. What did you expect to see? (Required)

Lightning to not fail if region split are suspended because of EBS BR

3. What did you see instead (Required)

Lightning failed

4. What is your TiDB version? (Required)

6.5

[D3Hunter]

failed to split: Err(Error(Kv(Error(Other(\\\"[src/server/raftkv/raft_extension.rs:128]: oneshot canceled\\\")))))\" "]

the error happens when doing EBS based backup, in which lightning don't support it