Support resolve blocking of DMLs when one worker doesn't see all shard DDLs

[lance6716]

Feature Request

Is your feature request related to a problem? Please describe:

DM source reading

The main processing logic of pessimistic sharding DDL is

1. one DM-worker handles one upstream MySQL. When it reads a sharding DDL, it will block replicating DMLs of this shard and continue reading binlog, until all shards of this upstream MySQL have sent sharding DDL. At that time DM-worker will stop replicating, build a DDL lock and wait for DM-master to coordinate and resolve it
2. DM-master waits for all DM-worker to build the DDL lock (if shards are splitted among N upstream sources, there should be N DM-worker to build the lock), let first DM-worker execute the DDL downstream and resolve all locks so DM-worker will continue to replicate binlog.

currently unlock-ddl-lock command is used to forcibly let DM-master resolve a lock. But when DM-worker doesn't see DDLs of all shard tables in its upstream, it didn't build a lock so there's no way to resolve blocking of shard tables whose sharding DDL has been seen.

Describe the feature you'd like:

Resolve above issue.

currently most related command is unlock-ddl-lock, but the parameter of this command is "lock ID" which is shown in show-ddl-locks. There's no "lock ID" when not see DDLs of all shard.

maybe we can propose a new command?

shard-ddl-lock
show ddl lock and partial synchronized sharding DDLs

shard-ddl-lock unlock <task> <-d target-database> <-t target-table> [--no-exec]
expect that the blocking of DML is resolved after this command

shard-ddl-lock inject <task> [-s source-id] <-d target-database> <-t target-table>
ignore unseen shard tables, build a DDL lock now

And I think for shard-ddl-lock unlock we can let DM-master to execute the DDL, to get rid of owner parameter of old unlock-ddl-lock.

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy:

[lance6716]

@GMHDBJD @lichunzhu PTAL about how to resolve this issue