WIP: Use knapsack from Gemfile

Open username-removed-128633 requested to merge remove-knapsack-from-gemfile into master

What does this MR do?

I'm retrying !12753 (merged) but with using the knapsack Rake tasks...

Are there points in the code the reviewer needs to double check?

We need to keep installing knapsack globally (i.e. using gem install knapsack), so let's remove it from the Gemfile, and be sure to disable knapsack

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

What are the relevant issue numbers?