[#24818] YSQL: Add a test guc to fail drop commands

Summary:
Add a test guc `yb_test_fail_all_drops` to fail all drop commands.
The GUC can be set per-session by a superuser.
Jira: DB-13922

Test Plan:
Manually tested.

```
yugabyte=# CREATE TABLE test (t int);
CREATE TABLE
yugabyte=# CREATE VIEW test2 AS SELECT * FROM test;
CREATE VIEW
yugabyte=# CREATE INDEX test3 ON test(t);
CREATE INDEX
yugabyte=# SET yb_test_fail_all_drops=true;
SET
yugabyte=# DROP INDEX test3;
ERROR:  TEST: failed drop operation as requested
HINT:  GUC yb_test_fail_all_drops is set to true.
yugabyte=# DROP VIEW test2;
ERROR:  TEST: failed drop operation as requested
HINT:  GUC yb_test_fail_all_drops is set to true.
yugabyte=# DROP TABLE test;
ERROR:  TEST: failed drop operation as requested
HINT:  GUC yb_test_fail_all_drops is set to true.
yugabyte=# RESET yb_test_fail_all_drops;
RESET
yugabyte=#  DROP INDEX test3;
DROP INDEX
yugabyte=# DROP VIEW test2;
DROP VIEW
yugabyte=# DROP TABLE test;
DROP TABLE
```

Reviewers: telgersma

Reviewed By: telgersma

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D39772

src/postgres/src/backend/tcop/utility.c

@@ -2102,6 +2102,12 @@ ProcessUtilityForAlterTable(Node *stmt, AlterTableUtilityContext *context)
 static void
 ExecDropStmt(DropStmt *stmt, bool isTopLevel)
 {
+	if (yb_test_fail_all_drops && isTopLevel)
+		ereport(ERROR,
+				(errcode(ERRCODE_INTERNAL_ERROR),
+				 errmsg("TEST: failed drop operation as requested"),
+				 errhint("GUC yb_test_fail_all_drops is set to true.")));
+
 	switch (stmt->removeType)
 	{
 		case OBJECT_INDEX:

src/postgres/src/backend/utils/misc/guc.c

@@ -2586,6 +2586,17 @@ static struct config_bool ConfigureNamesBool[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"yb_test_fail_all_drops", PGC_SUSET, DEVELOPER_OPTIONS,
+			gettext_noop("When set, all drops will fail"),
+			NULL,
+			GUC_NOT_IN_SAMPLE
+		},
+		&yb_test_fail_all_drops,
+		false,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"yb_test_fail_next_inc_catalog_version", PGC_USERSET,DEVELOPER_OPTIONS,
 			gettext_noop("When set, the next increment catalog version will "

src/postgres/src/backend/utils/misc/pg_yb_utils.c

@@ -1662,6 +1662,8 @@ bool yb_test_system_catalogs_creation = false;
 
 bool yb_test_fail_next_ddl = false;
 
+bool yb_test_fail_all_drops = false;
+
 bool yb_test_fail_next_inc_catalog_version = false;
 
 double yb_test_ybgin_disable_cost_factor = 2.0;

src/postgres/src/include/pg_yb_utils.h

@@ -647,6 +647,9 @@ extern bool yb_test_system_catalogs_creation;
  */
 extern bool yb_test_fail_next_ddl;
 
+/* If set to true, all drop commands will fail. */
+extern bool yb_test_fail_all_drops;
+
 /*
  * If set to true, next increment catalog version operation will fail and
  * reset this back to false.