build: update website dependencies, doc: fix markdown linter warnings in faq

[JakobLichterfeld]

• chore: update @docusaurus/core and @docusaurus/preset-classic dependencies to v3.4.0, and react and react-dom to v18.3.1
• build: specify node.js version for Netlify in base dir as latest lts major version
• doc: fix markdown linter warnings in faq

This fixes several security vulnerable:

• https://github.com/teslamate-org/teslamate/security/dependabot/1
• https://github.com/teslamate-org/teslamate/security/dependabot/18
• https://github.com/teslamate-org/teslamate/security/dependabot/36
• https://github.com/teslamate-org/teslamate/security/dependabot/37
• https://github.com/teslamate-org/teslamate/security/dependabot/40
• https://github.com/teslamate-org/teslamate/security/dependabot/44
• https://github.com/teslamate-org/teslamate/security/dependabot/46
• https://github.com/teslamate-org/teslamate/security/dependabot/47

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[JakobLichterfeld]

I introduced .node-version to let Netlify know, which node.Js version to use according to https://docs.netlify.com/configure-builds/manage-dependencies/#node-js-and-javascript