ewelink: websocket instead of poll

[atrovato]

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 (french forum/english forum) 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!

[cloudflare-workers-and-pages]

Deploying with    Cloudflare Pages

Latest commit:	b8bb148
Status:	⚡️  Build in progress...

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.39%. Comparing base (185fe8a) to head (589bd11).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #109      +/-   ##
==========================================
+ Coverage   98.32%   98.39%   +0.06%     
==========================================
  Files         836      860      +24     
  Lines       13269    13469     +200     
==========================================
+ Hits        13047    13253     +206     
+ Misses        222      216       -6     

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