[Docker] Alpine image fix (#9118)

* Revert to alpine3:20 / postgres:16

* Remove old hack

- No longer needed as we are using python 3.11

* Update package requirements for devcontainer

Also fixes some docker warnings from the alpine Dockerfile

* Specify SITE_URL

* Reduce log output during docker image testing

.devcontainer/Dockerfile

@@ -27,7 +27,7 @@ RUN apt update && apt install -y \
    postgresql-client \
    libldap2-dev libsasl2-dev \
    libpango1.0-0 libcairo2 \
-   weasyprint
+   poppler-utils weasyprint
 
 # Install packages required for frontend development
 RUN apt install -y \