[FEATURE] Optionally disable execution

[MathiasSven]

Is your feature request related to a problem? Please describe.
I have accumulated multiple code blocks in my notes, but some code blocks are not meant to be run, just viewed. Running them might simply just produce an error, or might end up creating needless files, change user configurations, and alter state I didn't mean to. Usually for me, it is obvious which code blocks are meant to be run because I tend to add a bunch of echo's or logging facilities, but it would be nice if this guesswork wasn't there.

Describe the solution you'd like
Add a way to disable the rendering of the Run button based on something like this:

```norun-python

or

```python {active=false}

where {active=true} by default

Describe alternatives you've considered
Removing the language next to backticks, but that removes syntax highlighting.

[sbhal]

An alternative could be live preview mode which doesn't show Run button with language next to backticks.