fix(schema): ignore empty string in app.{rootId|rootTag}

[DamianGlowala]

🔗 Linked issue

Resolves #22525

❓ Type of change

• 📖 Documentation (updates to the documentation, readme or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This PR ignores passing empty string for app.rootId and app.rootTag.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

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[Lehoczky]

Regarding the discussion in #22525: shall we update the code to validate using a regex, like one suggested in this stackoverflow thread?

[danielroe]

I'd be happy with that. 👍

[DamianGlowala]

A separate PR to address the id validation is very much welcome! I wanted to keep these separate, as this PR also ignores an empty string for app.rootTag.

(Well, if Daniel says so, we can update this one as well)

BTW we could go even further and validate the HTML tag (if this brings any value).

[danielroe]

I think simple validation could be good and maybe even normalisation (e.g. trimming whitespace?), but nothing too complex. Objective is to prevent obvious errors rather than provide a fully safe validation.