auto GTID mode

[actiontech-bot]

Is your feature request related to a problem? Please describe.
No

Describe the solution you'd like
if set GTID to "AUTO", like MySQL do, target should detect source's GTID and start replication from it

Describe alternatives you've considered
None

[ghost]

c917051: add AutoGtid for test use

Usage:

In job.json

• keep Gtid and GtidStart empty
• set "AutoGtid": true

TODO

• MySQLDriverConfig.Gtid is used as both
  • a task config for where to start
  • and a value for saving progress.
• which is a poor design