Add tutorial provider

[kissiel]

Description

This PR introduces a Checkbox Tutorial Provider.
The included test plan contains various jobs that yield different outcomes, including outcomes that are results of failing resources or dependent jobs.

Tested throughout manually 👨‍🔧

Resolves: CHECKBOX-750

[pieqq]

One question inline, and also one request: as I pointed out in Jira, I need a job that uses an environment variable (with a default set), because of this section in the tutorial.

So basically a job that runs something like

echo ${TUTO:-default}

so that it still outputs something if no env var is set, but behaves differently if an env var is set (in launcher, in my case).

[pieqq]

Another request for this PR: the tutorial needs to be available from an installed snap, so the snapcraft.yaml recipes need to package it, the same way we package provider-sru for instance.

[pieqq]

I've made the modifications I talked about in my review, and a few other things.

I've also added this provider to the checkbox22 snap. Not sure if it's useful to add it to others. Thoughts on that?

Finally, regarding the jobs, I'm wondering if we should drop the description fields and replace them with summary, since the latter will be used in the UI, but not the former.

[pieqq]

Revisiting this:

• yes, description should be replaced by summary, otherwise user will see job ids in the test selection screen
• a manual job is needed to show the user how to proceed with them
• probably also need a user-interact and a user-interact-verify job as well

[pieqq]

I've done the following:

• Add 3 interactive jobs (manual, user-interact and user-interact-verify) to demonstrate them when running the Tutorial test plan
• Add a Tutorial category so that our Tutorial jobs are not in the Uncategorised section of the test plan (it looked lame in the Tutorial page)
• Add some output to the passing and failing job for demonstration purposes (see Add "Running your first test plan" tutorial #705)
• Change description to summary so that we see a nice list of jobs summaries in the job selection screen

[tang-mm]

Changes in docs/ look good to me

[kissiel]

Thanks for picking up the branch!
One question below

[kissiel]

I can't officially +1 this PR as I opened it, but big +1 from me!

[pieqq]

Yay, I have to approve my own changes! Thank you GitHub!