Validate resources

[krzysztofrewak]

All resources should be automatically validated. It could be done in PHP or Javascript and then, added to GHA. I would expect:

• check if every resource has proper types (eg. not-nullable names for companies, nullable URLs for linkedin profiles, etc.)
• check if people and companies are sorted alphabetically (by company name and person surname and name) in their respective files
• check if all "relations" are valid (eg. if @marcintracz and @blumilk exist in people.json and companies.json:

    {
      "title": "xD bug - jak debugować PHP-owe aplikacje",
      "speakers": [
        {
          "person": "@marcintracz",
          "company": "@blumilk"
        }
      ]
    }

• image sizes and proportions?
• ... something more?