Add additional dependencies to ament_flake8. (#454)

The ROS 2 style guides and CI depend on all of the
following flake8 plugins:

python3-flake8-blind-except
python3-flake8-builtins
python3-flake8-class-newline
python3-flake8-comprehensions
python3-flake8-deprecated
python3-flake8-docstrings
python3-flake8-import-order
python3-flake8-quotes

However, we have classically not directly depended on these
anywhere.  Due to the plugin nature of flake8, this means
that the tests are just skipped if a user runs the tests
without them installed.  In turn, that means the errors only show
up when we run CI against their code, leading to user frustration.

To alleviate that, directly depend on the flake8 plugins that
we expect to exist.  This will ensure that they are automatically
installed when users do an installation.  The tradeoff is that
we'll increase the installation size for everyone by about 1MB, since
ament_flake8 is one of the core packages.

One other note is that 3 of the plugins are (still) disabled because
we have no packages on RHEL-9; that is being worked on and we'll enable
those once those packages are available.

Signed-off-by: Chris Lalancette <clalancette@gmail.com>

ament_flake8/package.xml

@@ -19,6 +19,17 @@
 
   <exec_depend>ament_lint</exec_depend>
   <exec_depend>python3-flake8</exec_depend>
+  <!-- TODO(clalancette): enable this once it is available in RHEL-9 -->
+  <!-- <exec_depend>python3-flake8-blind-except</exec_depend> -->
+  <exec_depend>python3-flake8-builtins</exec_depend>
+  <!-- TODO(clalancette): enable this once it is available in RHEL-9 -->
+  <!-- <exec_depend>python3-flake8-class-newline</exec_depend> -->
+  <exec_depend>python3-flake8-comprehensions</exec_depend>
+  <!-- TODO(clalancette): enable this once it is available in RHEL-9 -->
+  <!-- <exec_depend>python3-flake8-deprecated</exec_depend> -->
+  <exec_depend>python3-flake8-docstrings</exec_depend>
+  <exec_depend>python3-flake8-import-order</exec_depend>
+  <exec_depend>python3-flake8-quotes</exec_depend>
 
   <export>
     <build_type>ament_python</build_type>