Strip leading and trailing whitespace for unreleased_history entries (#11652)

Summary:
Some trailing whitespace has leaked into HISTORY.md entries. This can lead to unexpected changes when modifying HISTORY.md with hygienic editors (e.g. for a patch release). This change should protect against future cases.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11652

Test Plan: manual

Reviewed By: akankshamahajan15

Differential Revision: D47882814

Pulled By: pdillinger

fbshipit-source-id: 148c3746d3b298cb6e1f655f0416d46619969086

unreleased_history/release.sh

@@ -34,8 +34,12 @@ awk '/#define ROCKSDB_MAJOR/ { major = $3 }
 echo " (`date +%x`)" >> HISTORY.new
 
 function process_file () {
-  # use awk to correct extra or missing newlines, missing '* ' on first line
-  awk '/./ { if (notfirstline || $1 == "*") print;
+  # use awk to correct
+  # * extra or missing newlines
+  # * leading or trailing whitespace
+  # * missing '* ' on first line
+  awk '/./ { gsub(/^[ \t]+/, ""); gsub(/[ \t]+$/, "");
+             if (notfirstline || $1 == "*") print;
              else print "* " $0;
              notfirstline=1; }' < $1 >> HISTORY.new
   echo git rm $1