fixed "command is missing" while trying to create a command

[xFuture603]

I tried to create a new command for Icinga with a command_template_object in which the command was already specified and a command_object that should inherit properties from the template object. But I always got this error: "state is present but all of the following are missing: command", It turned out that the "required_if" (changed in this pr) led to this error.

[codecov]

Codecov Report

Merging #69 (3e75efe) into master (53fbf6e) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #69   +/-   ##
=======================================
  Coverage   93.71%   93.71%           
=======================================
  Files          17       17           
  Lines         493      493           
  Branches       47       47           
=======================================
  Hits          462      462           
  Misses          9        9           
  Partials       22       22           

Impacted Files	Coverage Δ
plugins/modules/icinga_command.py	95.65% <100.00%> (ø)

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[rndmh3ro]

Thanks!