Use package's found variable in the config script

Since "find_dependency" sets the found variable to false, this can be
used to conveniently check at the end before including the export set
whether all dependencies were found in a non-REQUIRED call.

This requires setting the <name>_FOUND variable to true at the start of
the file, because "find_dependency" sets the variable only if something
could not be found.

cmake-init/templates/common/cmake/install-config.cmake

@@ -1,6 +1,8 @@
-{% if pm %}include(CMakeFindDependencyMacro)
+{% if pm %}set({= name =}_FOUND YES)
+
+include(CMakeFindDependencyMacro)
 find_dependency({% if c %}json-c{% else %}fmt{% end %})
 
-if({% if c %}json-c{% else %}fmt{% end %}_FOUND)
+if({= name =}_FOUND)
   {% end %}include("${CMAKE_CURRENT_LIST_DIR}/{= name =}Targets.cmake"){% if pm %}
 endif(){% end %}

cmake-init/templates/common/cmake/install-rules.cmake

@@ -12,7 +12,8 @@ set(CMAKE_INSTALL_LIBDIR lib CACHE PATH ""){% end %}
 include(CMakePackageConfigHelpers)
 include(GNUInstallDirs)
 
-# find_package(<package>) call for consumers to find this project
+# find_package(<package>) call for consumers to find this project{% if pm %}
+# should match the name of variable set in the install-config.cmake script{% end %}
 set(package {= name =})
 
 install(