[pg15] fix: intermittent memory leak failure in initdb in asan

Summary:
The test CreateInitialSysCatalogSnapshot intermittently fails on asan build with the following stack trace:

   [m-1]     #1 0x5578be7959dc in pg_realloc /home/centos/code/yugabyte-db/src/postgres/src/common/../../../../../src/postgres/src/common/fe_memutils.c:72:8
   [m-1]     #2 0x5578be77b6b1 in readfile /home/centos/code/yugabyte-db/src/postgres/src/bin/initdb/../../../../../../src/postgres/src/bin/initdb/initdb.c:537:23
   [m-1]     #3 0x5578be77837b in bootstrap_template1 /home/centos/code/yugabyte-db/src/postgres/src/bin/initdb/../../../../../../src/postgres/src/bin/initdb/initdb.c:1434:14

This happens because during the execution of `bootstrap_template1()` in initdb, `bki_lines` first points to the memory allocated by readfile(). It then points to the memory allocated by replace_token(), without freeing the memory it was previously pointing to. Fix the issue by freeing up the memory allocated by readfile().

Note that there are more instances of memory leakage in initdb that are not detected by asan runs for some reason. For instance, memory allocated by replace_token() is never freed. These leakages are present in the YB master branch and upstream PG as well. Upstream PG doesn't care about it (https://www.postgresql.org/message-id/28473.1582440206%40sss.pgh.pa.us). The same reasoning applies to YB too. Also to prevent unnecessary deviation from PG code, we can let them remain.

Test Plan:
Jenkins: rebase: pg15
   ./yb_build.sh asan --cxx-test create_initial_sys_catalog_snapshot --gtest_filter CreateInitialSysCatalogSnapshotTest.CreateInitialSysCatalogSnapshot -n 100

Reviewers: jason

Reviewed By: jason

Subscribers: svc_phabricator, yql

Differential Revision: https://phorge.dev.yugabyte.com/D37736

src/postgres/src/bin/initdb/initdb.c

@@ -1427,11 +1427,13 @@ bootstrap_template1(void)
 	char	  **bki_lines;
 	char		headerline[MAXPGPATH];
 	char		buf[64];
+	char	  **yb_orig_bki_lines;
 
 	printf(_("running bootstrap script ... "));
 	fflush(stdout);
 
 	bki_lines = readfile(bki_file);
+	yb_orig_bki_lines = bki_lines;
 
 	/* Check that bki file appears to be of the right version */
 
@@ -1510,6 +1512,13 @@ bootstrap_template1(void)
 
 	free(bki_lines);
 
+	/*
+	 * YB note: free the memory allocated by readfile(), if not done already.
+	 * Without this, initdb fails on ASAN intermittently.
+	 */
+	if (yb_orig_bki_lines != bki_lines)
+		free(yb_orig_bki_lines);
+
 	check_ok();
 }