Upgrade ESLint configuration + preact-cli + preact

[Pierre-Gilles]

Pull Request check-list

To ensure your Pull Request can be accepted as fast as possible, make sure to review and check all of these items:

• If your changes affects code, did your write the tests?
• Are tests passing? (npm test on both front/server)
• Is the linter passing? (npm run eslint on both front/server)
• Did you run prettier? (npm run prettier on both front/server)
• If you are adding a new features/services, did you run integration comparator? (npm run compare-translations on front)
• Did you test this pull request in real life? With real devices? If this development is a big feature or a new service, we recommend that you provide a Docker image to the community for testing before merging.
• If your changes modify the API (REST or Node.js), did you modify the API documentation? (Documentation is based on comments in code)
• If you are adding a new features/services which needs explanation, did you modify the user documentation? See the GitHub repo and the website.
• Did you add fake requests data for the demo mode (front/src/config/demo.js) so that the demo website is working without a backend? (if needed) See https://demo.gladysassistant.com.

NOTE: these things are not required to open a PR and can be done afterwards / while the PR is open.

Description of change

Please provide a description of the change here. It's always best with screenshots, so don't hesitate to add some!

[codecov]

Codecov Report

Merging #1520 (3d49b66) into master (2588389) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1520   +/-   ##
=======================================
  Coverage   96.57%   96.57%           
=======================================
  Files         618      618           
  Lines        8992     8992           
=======================================
  Hits         8684     8684           
  Misses        308      308           

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[relativeci]

Job #300: Bundle Size — 6.72MB (-1.56%).

5bc2f0a vs 9295c33

Changed metrics (8/10)

Metric	Current	Baseline
Initial JS	2.85MB(-2.87%)	2.94MB
Initial CSS	294.27KB(-5.46%)	311.27KB
Cache Invalidation	77.01%	0%
Assets	139(+0.72%)	138
Modules	1168(+3.55%)	1128
Duplicate Code	0.48%(+2.13%)	0.47%
Packages	124(+7.83%)	115
Duplicate Packages	10(+900%)	1

Changed assets by type (3/7)

	Current	Baseline
CSS	312.21KB (-5.65%)	330.89KB
HTML	13.58KB (-4.64%)	14.24KB
JS	4.84MB (-1.79%)	4.92MB

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View Job #300 report on app.relative-ci.com