Simplify the docs for installing via terraform

[addyess]

Overview

Ensure that the user provides a deployment channel for the charms rather than rely on a default in the charm modules.

Details

• stop ignoring the channel field, and make the user provide one -- one that matches for both charms
• source the tf modules from github rather than locally checked out modules
• indicates one should run terraform plan before running apply

[bschimke95]

LGTM, minor nit

[louiseschmidtgen]

Thanks for the improvement of my docs! Some questions here:

[louiseschmidtgen]

I don't quite like this variable declaration here. First it should be in an input file and second this should be closer to where it is set >> sub-module.

[addyess]

so, this channel likely should match both k8s and k8s-worker. We can eliminate this from the example if you think that's a good idea and have folks go read the individual tf modules to learn what variables are optional.

i was trying to use this variable as var.k8s.channel for both modules. Did i do this incorrectly?

[addyess]

another thing, i wish i could use {{channel}} here

[addyess]

@louiseschmidtgen did i close the gap here or are we still an open issue. I'm unsure how to resolve

[nhennigan]

From a docs perspective this looks fine. I'll let Louise give the final approval as the terraform expert