Support generate difference backup with log backup

[3pointer]

Feature Request

Describe your feature request related problem:

Part of #325, After https://github.com/pingcap/ticdc/issues/768 TiCDC support external storage. we have the ability to generate lots of log backup with TiCDC. but sometimes, the log is too large to apply. mostly, users prefer a difference backup rather than log backup. so we can directly translate log backup to sst file. and this will improve the performance of data recovery.

Describe the feature you'd like:

Support generate difference backup(SST can be restored) with log backup.

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy:

Workload estimation(person-day)

• Design: 1
• Develop: 5
• QA: 3
• Document: 3

[kennytm]

Are we going to need a spare TiKV cluster for this? The main issue about constructing the SST file. This is similar to Lightning Local Backend which streams sorted KV pairs to TiKV at the end because we are not sure that cockroachdb/pebble is able to create SSTs acceptable by TiKV.

[3pointer]

Are we going to need a spare TiKV cluster for this? The main issue about constructing the SST file. This is similar to Lightning Local Backend which streams sorted KV pairs to TiKV at the end because we are not sure that cockroachdb/pebble is able to create SSTs acceptable by TiKV.

I think we can use a TiKV cluster to generate SST to s3 storage. it's easy to use.