[test](jdbc)add new case for mysql external table

[lsy3993]

Proposed changes

Issue Number: close #xxx

Problem summary

Describe your changes.

Checklist(Required)

1. Does it affect the original behavior:
   • Yes
   • No
   • I don't know
2. Has unit tests been added:
   • Yes
   • No
   • No Need
3. Has document been added or modified:
   • Yes
   • No
   • No Need
4. Does it need to update dependencies:
   • Yes
   • No
5. Are there any changes that cannot be rolled back:
   • Yes (If Yes, please explain WHY)
   • No

Further comments

If this is a relatively large or complex change, kick off the discussion at dev@doris.apache.org by explaining why you chose the solution you did and what alternatives you considered, etc...

[hello-stephen]

TeamCity pipeline, clickbench performance test result:
the sum of best hot time: 35.44 seconds
load time: 446 seconds
storage size: 17171334860 Bytes
https://doris-community-test-1308700295.cos.ap-hongkong.myqcloud.com/tmp/20221124033814_clickbench_pr_51799.html

[morningman]

LGTM