Set hidden Oracle parameters

[nblxa]

Is your feature request related to a problem? Please describe.
Unfortunately there are applications that require undocumented hidden Oracle parameters with names starting with the underscore. I would like El Carro to offer the possibility to define these in the Instance resource.

Describe the solution you'd like
It should be possible to set hidden parameters in the Instance resource, preferably but not necessarily similar to how it is done for the regular ones.

Describe alternatives you've considered
Run a custom SQL script during the database image creation.

Additional context
Since it is not possible to look up the type of hidden parameters in V$PARAMETER there should be a way of determining the type otherwise. One possible way could be to let user specify the type, but then hidden parameters will use a different YAML syntax than parameters currently. In such case it could be possible to let user define the scope as well. Otherwise the scope has to default to "spfile".