Fix pkg_mgr_name fact finding for Fedora (#40922)

* Properly handle default package manager vs apt

For distros where apt might be installed but is not the default
package manager for the distro, properly identify the default distro
package manager during fact finding and re-use fact finding from
DistributionFactCollector and instead of reimplementing small
portions of it in PkgMgrFactCollector

Add unit test to always check the apt + Fedora combination to test
the new code.

Fixes #34014

Signed-off-by: Adam Miller <admiller@redhat.com>

* remove q debugging output I accidentally left behind

Signed-off-by: Adam Miller <admiller@redhat.com>

* add os_family to the conditional so we're only hitting that code path when needed

Signed-off-by: Adam Miller <admiller@redhat.com>

* setup for a _check* pattern for general os_family group pkg_mgr checking

Signed-off-by: Adam Miller <admiller@redhat.com>

* use Mock.patch decorator for os.path.exists in TestPkgMgrFactsAptFedora

Signed-off-by: Adam Miller <admiller@redhat.com>

test/integration/targets/package/tasks/main.yml

@@ -24,11 +24,33 @@
 - name: create our testing sub-directory
   file: path="{{ output_dir_test }}" state=directory
 
+# Verify correct default package manager for Fedora
+# Validates: https://github.com/ansible/ansible/issues/34014
+- block:
+    - name: install apt
+      dnf:
+        name: apt
+        state: present
+    - name: gather facts again
+      setup:
+    - name: validate output
+      assert:
+        that:
+          - 'ansible_pkg_mgr == "dnf"'
+  always:
+    - name: remove apt
+      dnf:
+        name: apt
+        state: absent
+    - name: gather facts again
+      setup:
+  when: ansible_distribution == "Fedora"
+
 ##
 ## package
 ##
 
-- name: define distros to attempt installing at on 
+- name: define distros to attempt installing at on
   set_fact:
     package_distros:
         - RedHat