cmake: install mgr module separately

cmake: install mgr module separately

instead of installing the whole directory, install mgr modules
individually, so it's more clear that what EXCLUDE pattern is
used in which mgr module.

this improves the maintability and readability. in future, we
should only install the artifacts. with this change, we can
specify the include pattern only for dashboard mgr module so
that, for instance, only .js, .html and .css files are installed.

Signed-off-by: Kefu Chai <kchai@redhat.com>