Improve Docker-Compose Install Experience (#9781)

This PR updates the docker-compose installation documentation and env
sample to improve the setup experience.

- Updates the URLs for raw files to reference main branch, which is
likely where new users will be pulling from initially. This seems to be
the most straightforward option; assume that advanced users who want to
retrieve it from a particular tag will know to change the URL for their
scenario.
- Fixes an improperly stated curl command.
- Adds a note that the PGPASSWORD_SUPERUSER should be URL-safe. This is
required since the value is later concat into a PG_DATABASE_URL as a
URL, and expected to be in proper URL format. Touches on #8597.

---------

Co-authored-by: Félix Malfait <felix@twenty.com>
Co-authored-by: Félix Malfait <felix.malfait@gmail.com>

.github/workflows/ci-test-docker-compose.yaml

@@ -39,7 +39,7 @@ jobs:
           echo "Generating secrets..."
           echo "# === Randomly generated secrets ===" >>.env
           echo "APP_SECRET=$(openssl rand -base64 32)" >>.env
-          echo "PGPASSWORD_SUPERUSER=$(openssl rand -base64 32)" >>.env
+          echo "PGPASSWORD_SUPERUSER=$(openssl rand -hex 16)" >>.env
 
           echo "Docker compose up..."
           docker compose up -d || {