DISC: Revise Execution Options `jupyter_execute_nb` and `jupyter_execute_notebooks`

[mmcky]

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@AakashGfude. I am tidying up while writing documentation. We have both:

jupyter_execute_nb and jupyter_execute_notebooks. Are these redundant?

I think I prefer to use jupyter_execute_notebooks which is slightly more verbose but also more descriptive.

[AakashGfude]

jupyter_execute_nb is an object at present which has the following structure

{
        "no-text" : True,
        "timeout" : 600,
        "text_reports" : True,
        "coverage" : False,
}

We will remove this and reorganize its keys as a part of the issue 199

[mmcky]

I see - thanks @AakashGfude