MINOR: Add co-authors to release email template (apache#14080)

Reviewers: Mickael Maison <mickael.maison@gmail.com>

release.py

@@ -332,8 +332,8 @@ def command_release_announcement_email():
         validate_release_num(previous_release_version_num)
     if release_version_num < previous_release_version_num :
         fail("Current release version number can't be less than previous release version number")
-    number_of_contributors = int(subprocess.check_output('git shortlog -sn --no-merges %s..%s | wc -l' % (previous_release_version_num, release_version_num) , shell=True).decode('utf-8'))
-    contributors = subprocess.check_output("git shortlog -sn --no-merges %s..%s | cut -f2 | sort --ignore-case" % (previous_release_version_num, release_version_num), shell=True).decode('utf-8')
+    number_of_contributors = int(subprocess.check_output('git shortlog -sn --group=author --group=trailer:co-authored-by --no-merges %s..%s | uniq | wc -l' % (previous_release_version_num, release_version_num) , shell=True).decode('utf-8'))
+    contributors = subprocess.check_output("git shortlog -sn --group=author --group=trailer:co-authored-by --no-merges %s..%s | cut -f2 | sort --ignore-case | uniq" % (previous_release_version_num, release_version_num), shell=True).decode('utf-8')
     release_announcement_data = {
         'number_of_contributors': number_of_contributors,
         'contributors': ', '.join(str(x) for x in filter(None, contributors.split('\n'))),
@@ -391,7 +391,7 @@ def command_release_announcement_email():
 Capital One, Goldman Sachs, ING, LinkedIn, Netflix, Pinterest, Rabobank,
 Target, The New York Times, Uber, Yelp, and Zalando, among others.
 
-A big thank you for the following %(number_of_contributors)d contributors to this release!
+A big thank you for the following %(number_of_contributors)d contributors to this release! (Please report an unintended omission)
 
 %(contributors)s
 
@@ -404,7 +404,8 @@ def command_release_announcement_email():
 
 Regards,
 
-<YOU>""" % release_announcement_data
+<YOU>
+Release Manager for Apache Kafka %(release_version)s""" % release_announcement_data
 
     print()
     print("*****************************************************************")