NodeJS support policy and CI improvements

.github/auto-issue-templates/new-node-lts.md

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+# New Node.js LTS version detected
+
+_Issue created automatically by a Github action._
+
+A new Node.js LTS version has been detected: `{{ steps.check-version.outputs.new_lts_version }}`.
+
+Please test the Log4brains project against this version and update the supported versions accordingly.
+
+- [ ] Update the LTS version in `.nvmrc`
+- [ ] Run `nvm use` and ensure `node -v` returns the new LTS version
+- [ ] Run `rm -rf node_modules && yarn install`
+- [ ] Run all the quality checks described in CONTRIBUTNG.md
+- [ ] Run and test the app manually
+- [ ] Fix the potential bugs
+- [ ] Update `.github/supported_nodejs_versions.json`: add the new LTS version and remove the ones that are no longer supported (see [Node.js release schedule](https://github.com/nodejs/release#release-schedule))
+- [ ] Update all `engine.node` fields in `package.json` files

.github/supported_nodejs_versions.json

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+{
+  "versions": ["18.x", "20.x"]
+}