[Documentation] Add CLI switch to opt-out documentation (md) generation

[wing328]

Add a CLI switch (e.g. generateDoc) for generating documentation.

Default is true.

Related discussion: #2595, #2079

If anyone wants to work on this, please reply to let us know.

[jimschubert]

I have a pull open for this feature using options apiDocs and modelDocs in #2866.

[wing328]

PR merged. Thanks for the contribution from @jimschubert