biboumi: init at 6.1 (#30193)

* biboumi: init at 6.1

TODO: integrate config in NixOS

* biboumi: remove external buildtime dep

- fetch catch.hpp in a reproducible way
- add maintainer
- enable tests
- remove git dep
- enable parallel building
- add pandoc dep for man page
- nitpicks

* biboumi: refine substitutions

- only CMakeLists.txt has to be patched regarding /etc/biboumi
- substitute /bin/kill in systemd service file
- prepare for configuring policy_directory in a future cfg file

pkgs/servers/xmpp/biboumi/catch.patch

@@ -0,0 +1,30 @@
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -273,27 +273,6 @@ foreach(file ${source_all})
+ endforeach()
+ 
+ #
+-## Add a rule to download the catch unit test framework
+-#
+-include(ExternalProject)
+-ExternalProject_Add(catch
+-  GIT_REPOSITORY "https://lab.louiz.org/louiz/Catch.git"
+-  PREFIX "external"
+-  UPDATE_COMMAND ""
+-  CONFIGURE_COMMAND ""
+-  BUILD_COMMAND ""
+-  INSTALL_COMMAND ""
+-  )
+-set_target_properties(catch PROPERTIES EXCLUDE_FROM_ALL TRUE)
+-ExternalProject_Get_Property(catch SOURCE_DIR)
+-if(NOT EXISTS ${CMAKE_SOURCE_DIR}/tests/catch.hpp)
+-  target_include_directories(test_suite
+-    PUBLIC "${SOURCE_DIR}/include/"
+-    )
+-  add_dependencies(test_suite catch)
+-endif()
+-
+-#
+ ## Add some custom rules to launch the tests
+ #
+ add_custom_target(check COMMAND "test_suite"