chore(costmap_generator): add maintainers (autowarefoundation#2766)

* chore(costmap_generator): add maintainers

Signed-off-by: kosuke55 <kosuke.tnp@gmail.com>

* Update package.xml

---------

Signed-off-by: kosuke55 <kosuke.tnp@gmail.com>
Co-authored-by: Kenji Miyake <31987104+kenji-miyake@users.noreply.github.com>

planning/costmap_generator/package.xml

@@ -4,14 +4,15 @@
   <name>costmap_generator</name>
   <version>0.1.0</version>
   <description>The costmap_generator package</description>
-  <maintainer email="kenji.miyake@tier4.jp">Kenji Miyake</maintainer>
+  <maintainer email="kosuke.takeuchi@tier4.jp">Kosuke Takeuchi</maintainer>
+  <maintainer email="takamasa.horibe@tier4.jp">Takamasa Horibe</maintainer>
+  <maintainer email="takayuki.murooka@tier4.jp">Takayuki Murooka</maintainer>
+  <maintainer email="yutaka.shimizu@tier4.jp">Yutaka Shimizu</maintainer>
   <license>Apache License 2.0</license>
 
   <!-- Original license -->
   <license>BSD-3-Clause</license>
 
-  <author email="kenji.miyake@tier4.jp">Kenji Miyake</author>
-
   <buildtool_depend>ament_cmake_auto</buildtool_depend>
 
   <build_depend>autoware_cmake</build_depend>