More opiniated base image

[indyjonesnl]

The good

• Remove composer (smaller image size, we shouldn't have/use it on production pods, prevent attack vector on package manager)
• Provide default performance improvements out of the box:
  • realpath cache optimizations (as suggested by Symfony)
  • opcache "..."
• Default Caddyfile out of the box
  • Currently it allows for overwriting the log level of the Caddy application itself (server logging)
  • Currently it allows for overwriting the http log level (request logging)
• Default Google Cloud (JSON) format logging

The bad

We need to either copy Composer into the apps (defeating the point of excluding it from the base image), or mount it 'on-the-fly' using RUN --mount=type=bind,from=composer/composer:2-bin,source=/composer,target=/usr/local/bin/composer \ composer install

The ugly

Using a shared Caddyfile can introduce 1 bug into many microservices, though with this approach there would also be 1 bugfix. Duplicating a Caddyfile into >10 apps could decrease the risk of introducing a shared bug, but would also mean creating 10 fixes for 1 bug.