Fix Set-DbaAgentJobStep (#5030)

* Added option to add job step if it doesn't exist

* Added try/catch block for new job step
Moved job step settings

* Changed param type
Fixed if statement

* Removed comment in param

* Added else statements to alter the job step

* Fixed job check
Added filter for job and job step
Fixed check for job
Fixed check for Database and DatabaseUsername

* Changed if statements to better check for the variables

* Added subsystem server. Fixes #4715

* Formatted it to be the dbatools way

* Added check if Server value is set

* Reformatted the code

* Removed aliases

* Added parameter to unit test

* Added inputobject parameter

* Added help