Do not use --skip-update when running Kolibri in development mode

[jonboiser]

Summary

Changes the devserver npm scripts to use the python-devserver script, which invokes kolibri start without the --skip-update flag.

This means, when you start Kolibri after deleting your KOLIBRI_HOME folder, or updating the KOLIBRI_HOME variable, etc, running the devserver for the first time will create the dev database and run the migrations first.

This also uses the run-p shorthand to replace npm-run-all --parallel in the 4 scripts

I also updated the "Getting started" guide to explain this change to the onboarding experience as well as the KOLIBRI_HOME env variable.

Reviewer guidance

Check to see that this new script works in different common situations like:

1. Running Kolibri for the first time
2. Running Kolibri for a second time
3. Simulating an upgrade or a downgrade and running the devserver script.

References

Fixes #7302

Contributor Checklist

PR process:

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Testing:

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

Reviewer Checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[jonboiser]

@rtibbles What needs to be updated in the dev docs? I can just add it to this PR

[rtibbles]

@radinamatic had just added this: https://github.com/learningequality/kolibri/blob/develop/docs/getting_started.rst#database-setup because of this exact issue, but with this change it's now redundant :)

[radinamatic]

Oh, well... 🤷🏽‍♀️

Do we need to revert and delete the Database setup step now?

[jonboiser]

Do we need to revert and delete the Database setup step now?

I removed that section, but added some explanation that the database setup happens as part of the first yarn run devserver command.

Hopefully, after this change. The onboarding experience is simple as 1. clone the repo, 2. install deps, 3. yarn run devserver

[rtibbles]

@jonboiser not seeing the docs updates in this PR, did you push them?

[jonboiser]

Whoops, I did not!

[jonboiser]

Here's the diff that I did not push 😭

jonboiser@23cbb34

I can revisit this after #7940 is merged, just to make sure the whole onboarding story is documented consistently.

[rtibbles]

Have merged #7940