TYPO3 Core

The web based TYPO3 installer uses a already existing `additional.php`
configuration instead of asking for database connection configuration.
That is used to provide quick installation for automatic customer
instance deployments and the local development environment tool `ddev`
is also able to provide and manage this file. At least when [1] gets
merged also writing the correct file for TYPO3 v12+ projects in legacy
mode.

TYPO3 v12 introduced the `setup` command to setup a new installation,
but forces to provide database credentials along the way and ignores
an existing `additional.php` configuration setup.

[1] https://github.com/ddev/ddev/pull/6525

Can be tested with TYPO3 mono repository:

ddev config \
      --project-name 't3c-v13-mono' \
      --project-type 'typo3' \
      --docroot './' \
      --database 'mariadb:10.11' \
      --php-version '8.2' \
      --webserver-type 'apache-fpm' \
      --web-environment='TYPO3_CONTEXT=Development' \
  && ddev start \
  && ddev composer install \
  && ddev exec touch FIRST_INSTALL \
  && if [[ ! -f "typo3conf/system/additional.php" ]]; then mkdir -p "typo3conf/system" ; \cp -Rvf "typo3conf/AdditionalConfiguration.php" "typo3conf/system/additional.php"; fi \
  && ddev launch /typo3/install.php

versus

ddev config \
      --project-name 't3c-v13-mono' \
      --project-type 'typo3' \
      --docroot './' \
      --database 'mariadb:10.11' \
      --php-version '8.2' \
      --webserver-type 'apache-fpm' \
      --web-environment='TYPO3_CONTEXT=Development' \
  && ddev start \
  && ddev composer install \
  && ddev exec touch FIRST_INSTALL \
  && if [[ ! -f "typo3conf/system/additional.php" ]]; then mkdir -p "typo3conf/system" ; \cp -Rvf "typo3conf/AdditionalConfiguration.php" "typo3conf/system/additional.php"; fi \
  && ddev typo3 setup \
        --admin-username=john-doe \
        --admin-user-password='John-Doe-1701D.' \
        --admin-email="john.doe@example.com" \
        --project-name='new-page' \
        --no-interaction \
        --server-type=apache \
        --force