Icinga2 utility on CentOS fails to get version

Description of Issue

As mentioned already in #51862, get_certs_path() in salt/utils/icinga2.py fails to extract Icinga2 Version on a CentOS server and throws an error:

AttributeError: 'NoneType' object has no attribute 'group'

This happens because
version = re.search(r"r\d+\.\d+", icinga2_output["stdout"]).group(0)
doesn't find anything, since the version label in the output of icinga2 --version doesn't include the letter 'r' as on Ubuntu, probably in all of Debian family.
I suspect that it should work without the 'r' inside the regex in all of the RedHat family.

Setup

CentOS Linux 8.2.2004 Core
Icinga2 2.11.3

Steps to Reproduce Issue

salt-call icinga2.generate_cert HOSTNAME

Versions Report

Salt Version:
           Salt: 3000.3

Dependency Versions:
           cffi: 1.11.5
       cherrypy: Not Installed
       dateutil: 2.6.1
      docker-py: Not Installed
          gitdb: Not Installed
      gitpython: Not Installed
         Jinja2: 2.10.1
        libgit2: Not Installed
       M2Crypto: 0.35.2
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.6.2
   mysql-python: Not Installed
      pycparser: 2.14
       pycrypto: Not Installed
   pycryptodome: Not Installed
         pygit2: Not Installed
         Python: 3.6.8 (default, Apr 16 2020, 01:36:27)
   python-gnupg: Not Installed
         PyYAML: 3.12
          PyZMQ: 19.0.0
          smmap: Not Installed
        timelib: Not Installed
        Tornado: 4.5.3
            ZMQ: 4.3.2

System Versions:
           dist: centos 8.2.2004 Core
         locale: UTF-8
        machine: x86_64
        release: 4.18.0-193.6.3.el8_2.x86_64
         system: Linux
        version: CentOS Linux 8.2.2004 Core

Start in salt/utils/icinga2.py at get_certs_path() and inspect how the output of icinga2 --version is parsed. Reproduce with salt-call icinga2.generate_cert HOSTNAME on the reported CentOS/Icinga2 setup, then verify that version extraction no longer raises the reported AttributeError and supports the shown version format.