[Ruby] fix DateTime default value

[wing328]

To fix exception when DateTime property has a default value.

The updated code looks like the following:

      if attributes.key?(:'date')
        self.date = attributes[:'date']
      else
        self.date = Date.parse("2010-02-01")
      end

      if attributes.key?(:'date_time')
        self.date_time = attributes[:'date_time']
      else
        self.date_time = DateTime.parse("2010-02-01T09:20:10.111110Z[UTC]")
      end

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cc @cliffano (2017/07) @zlx (2017/09) @autopp (2019/02)

[jfeltesse-mdsol]

I guess it'll be for another PR but FYI DateTime in ruby is discouraged, see Matz' answer at https://bugs.ruby-lang.org/issues/15712#note-4

Also I'm not sure if the timestamp example is the way it's done in Java but the Z already denotes the UTC timezone so it strikes me as odd to have [UTC]. Maybe use a different timezone to ensure not only the default path that UTC is works?

[wing328]

Thanks for the review and sharing more. We'll need to replace DateTime with Time in another PR instead as this one aims to resolve the exception thrown due to datetime default value, which is a blocker for your work.

[wing328]

Filed #7656 to replace DateTime with Time