Tweak: Added a check if the user already exists for the "oe:admin:c…

[oxidMichaelWalter]

Tweak: Added a check if the user already exists for the "oe:admin:create" command

[CLAassistant]

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[Sieg]

Hey, @oxidMichaelWalter, need some rework here:

• In Dao, if we could be not so specific, we could use the method for more cases, how about making a method with the name getAdminUserByEmail or even better getByEmail as it already have "create"?
• Instead of checking for user existence in the AdminFactory (and EXIT? you cannot use exit), let's check for user existence in the command itself, near email validation maybe, and we could use getByEmail for this check.
• Also, where are the tests? ;) will not work for this case.