Add SHOW VSCHEMA KEYSPACES query

[GuptaManan100]

Description

This PR adds a new Vitess specific query syntax to vtgates, SHOW VSCHEMA KEYSPACES. This query is intended to print out the information of all the keyspaces that Vitess has. Specifically, this query prints out the keyspace name, whether it is sharded, what the foreign key management mode is and the error in the keyspace (if any).

This query is intended to provide an easier way to look at the keyspace information as an alternative to looking at the /debug/vschema endpoint of vtgate and finding the required information.

The query looks like the following when run from vtgate -

mysql> show vschema keyspaces;
+----------+---------+-------------+---------+
| Keyspace | Sharded | Foreign Key | Comment |
+----------+---------+-------------+---------+
| ks       | true    | managed     |         |
| uks      | false   | managed     |         |
+----------+---------+-------------+---------+
2 rows in set (0.01 sec)

Related Issue(s)

• Came up as part of Feature Request: Add support for foreign key mode managed to vttestserver #14495 (comment)

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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[harshit-gangal]

need to fix upgrade downgrade test

2023-11-10T09:17:03.2520559Z === RUN   TestInitAndUpdate
2023-11-10T09:17:03.3682409Z     st_sharded_test.go:195: 
2023-11-10T09:17:03.3683627Z         	Error Trace:	/home/runner/work/vitess/vitess/go/test/endtoend/utils/utils.go:153
2023-11-10T09:17:03.3686117Z         	            				/home/runner/work/vitess/vitess/go/test/endtoend/utils/utils.go:48
2023-11-10T09:17:03.3689435Z         	            				/home/runner/work/vitess/vitess/go/test/endtoend/vtgate/schematracker/sharded/st_sharded_test.go:195
2023-11-10T09:17:03.3690912Z         	Error:      	Received unexpected error:
2023-11-10T09:17:03.3692982Z         	            	syntax error at position 23 near 'KEYSPACES' (errno 1105) (sqlstate HY000) during query: SHOW VSCHEMA KEYSPACES
2023-11-10T09:17:03.3694454Z         	Test:       	TestInitAndUpdate
2023-11-10T09:17:03.3695102Z         	Messages:   	for query: SHOW VSCHEMA KEYSPACES
2023-11-10T09:17:03.3695708Z --- FAIL: TestInitAndUpdate (0.12s)