Progress Helper in Console component should mention setRedrawFrequency() instead of manual process

[dave1010]

components/console/helpers/progresshelper.rst currently says this:

For performance reasons, be careful to not set the total number of steps
to a high number. For example, if you're iterating over a large number
of items, consider a smaller "step" number that updates on only some
iterations

But ProgressHelper::setRedrawFrequency() exists (in 2.2, possibly before), which seems to do this for you.

[wouterj]

The ProgressHelper was new in 2.2, so I've given it a 2.2 milestone. I'm 👍 to document this (but still leave that message, as I think it's still relevant)