Unistore: Batch write events (#101381)

* Batch write events

* Improve instrumentation

* Measure batch phases

* Detect lock contention

* remove the execBatch goroutine

* removing tracing prefix

* detect context cancel

* batch channel map

pkg/storage/unified/sql/testdata/mysql--resource_update_rv-single path.sql

@@ -1,4 +1,10 @@
 UPDATE `resource`
-    SET `resource_version` = 0
-    WHERE  `guid` = ''
-;
+SET `resource_version` = (
+    CASE
+    WHEN `guid` = 'guid1' THEN CAST(123 AS SIGNED)
+    WHEN `guid` = 'guid2' THEN CAST(456 AS SIGNED)
+    END
+)
+WHERE `guid` IN (
+    'guid1', 'guid2'
+);