Support information_schema.schemata query

[lanchengx]

For #11994.

Changes proposed in this pull request:

• Currently only supports select * and SELECT column_name, ..., functions such as select count() are not supported.
  • Sample SQLs

    SELECT SCHEMA_NAME, DEFAULT_CHARACTER_SET_NAME, DEFAULT_COLLATION_NAME FROM information_schema.SCHEMATA;
    SELECT * FROM information_schema.SCHEMATA;

• The schema in the result is the schema in the proxy, and other data comes from a random database in the current schema.

[codecov-commenter]

Codecov Report

Merging #12011 (1f18f8b) into master (610ecd8) will decrease coverage by 0.00%.
The diff coverage is 82.55%.

@@             Coverage Diff              @@
##             master   #12011      +/-   ##
============================================
- Coverage     63.21%   63.20%   -0.01%     
  Complexity     1231     1231              
============================================
  Files          2300     2303       +3     
  Lines         34949    35024      +75     
  Branches       6086     6097      +11     
============================================
+ Hits          22094    22138      +44     
- Misses        11068    11095      +27     
- Partials       1787     1791       +4     

Impacted Files	Coverage Δ
.../text/admin/DatabaseAdminUpdateBackendHandler.java	0.00% <ø> (ø)
...n/mysql/MySQLInformationSchemaExecutorFactory.java	40.00% <40.00%> (ø)
...nd/text/admin/mysql/MySQLAdminExecutorFactory.java	55.55% <62.50%> (+12.69%)	⬆️
...text/admin/DatabaseAdminBackendHandlerFactory.java	69.23% <66.66%> (-5.77%)	⬇️
...l/executor/information/SelectSchemataExecutor.java	87.27% <87.27%> (ø)
...ackend/text/TextProtocolBackendHandlerFactory.java	72.97% <100.00%> (+2.38%)	⬆️
...ext/admin/mysql/enums/InformationSchemataEnum.java	100.00% <100.00%> (ø)
...sphere/scaling/core/job/schedule/JobScheduler.java	22.22% <0.00%> (-29.63%)	⬇️
...re/scaling/core/executor/engine/ExecuteEngine.java	88.88% <0.00%> (-11.12%)	⬇️
...scaling/core/job/task/inventory/InventoryTask.java	68.88% <0.00%> (-6.67%)	⬇️
... and 5 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 610ecd8...1f18f8b. Read the comment docs.