Improve sinks in UI (explain)

[nikvas0]

Show sink information (table and type) in YDB UI (explain: computation graph).

How sink JSON looks

ydb/ydb/tests/functional/canonical/canondata/test_sql.TestCanonicalFolder1.test_case_explain.script-script_/explain.script.plan

Line 537 in 38eb729

"SinkType": "KqpTableSink",

At current time sink nodes doesn't contain any info. Plan for query INSERT INTO new_order (NO_W_ID, NO_D_ID, NO_O_ID) VALUES (0, 0, 0) (main branch)

[nikvas0]

Info is in the Iterator node. I didn't notice it.
May be move this info to the Sink node instead of the Iterator node?

part of JSON plan

"Plans": [
            {
              "Tables": [
                "new_order"
              ],
              "PlanNodeId": 1,
              "Operators": [
                {
                  "Inputs": [],
                  "Iterator": "[{NO_D_ID: 0,NO_O_ID: 0,NO_W_ID: 0}]",
                  "Name": "Iterator"
                },
                {
                  "Inputs": [],
                  "Path": "/Root/db1/new_order",
                  "Name": "Insert",
                  "SinkType": "KqpTableSink",
                  "Table": "new_order"
                }
              ],
              "Node Type": "ConstantExpr-Sink"
            }
          ],