As I'm new, I can't comment directly on NeNaD's answer. Please be aware, that if you opt for this solution, this will replace your assets configuration you defined earlier in the general build options. If you don't want to replace the entire assets configuration but replace specific files based on the environment, work with fileReplacements, e.g.:

"build": {
    "configurations": {
        "production": {
            "fileReplacements": [
                {
                    "replace": "src/assets/seo/development/robots.txt",
                    "with": "src/assets/seo/production/robots.txt"
                },
                {
                    "replace": "src/assets/seo/development/sitemap.xml",
                    "with": "src/assets/seo/production/sitemap.xml"
                }
            ]
        }
    }
}

I hope this helps any one trying NeNaD's answer and wondering where their images went.