Scatter region will be restricted by the remove peer limit if the region is not empty

[rleungx]

Enhancement Task

Previously, we use light peer to skip the store limit check for the scatter region operator. But after we support the remove peer limit, we didn't take the light peer into consideration. When we scatter the non-empty region, the operator could be limited and directly canceled.

[2023/06/09 12:20:06.536 +08:00] [INFO] [cluster_worker.go:145] ["alloc ids for region split"] [region-id=1293] [peer-ids="[1294]"]
[2023/06/09 12:20:06.548 +08:00] [INFO] [cluster_worker.go:237] ["region batch split, generate new regions"] [region-id=222] [origin="id:1287 start_key:\"7480000000000081FFD95F72FFFFFFFFFFFFFFFFFF0000000000FB\" end_key:\"7480000000000081FFF25F698000000000FF000001FB00000000FB\" region_epoch:<conf_ver:25 version:191 > peers:<id:1288 store_id:10 > id:1289 start_key:\"7480000000000081FFF25F698000000000FF000001FB00000000FB\" end_key:\"7480000000000081FFF25F698000000000FF000002FB00000000FB\" region_epoch:<conf_ver:25 version:191 > peers:<id:1290 store_id:10 > id:1291 start_key:\"7480000000000081FFF25F698000000000FF000002FB00000000FB\" end_key:\"7480000000000081FFF25F698000000000FF000003FB00000000FB\" region_epoch:<conf_ver:25 version:191 > peers:<id:1292 store_id:10 > id:1293 start_key:\"7480000000000081FFF25F698000000000FF000003FB00000000FB\" end_key:\"7480000000000081FFF25F698000000000FF000004FB00000000FB\" region_epoch:<conf_ver:25 version:191 > peers:<id:1294 store_id:10 > id:1295 start_key:\"7480000000000081FFF25F698000000000FF000004FB00000000FB\" end_key:\"7480000000000081FFF25F72FFFFFFFFFFFFFFFFFF0000000000FB\" region_epoch:<conf_ver:25 version:191 > peers:<id:1296 store_id:10 >"] [total=5]
[2023/06/09 12:20:06.610 +08:00] [INFO] [operator_controller.go:611] ["operator canceled"] [region-id=1293] [takes=0s] [operator="\"scatter-region {mv light peer: store [10] to [4]} (kind:admin,region,leader, region:1293(191, 25), createAt:2023-06-09 12:20:06.610477352 +0
800 CST m=+1961.716996864, startAt:0001-01-01 00:00:00 +0000 UTC, currentStep:0, size:22, steps:[add learner peer 1299 on store 4, use joint consensus, promote learner peer 1299 on store 4 to voter, demote voter peer 1294 on store 10 to learner, transfer leader from store
 10 to store 4, leave joint state, promote learner peer 1299 on store 4 to voter, demote voter peer 1294 on store 10 to learner, remove peer on store 10]，timeout:[18m0s])\""] [additional-info=]

Related to pingcap/tidb#44550