fix: Fix signatures export from initiatives

[AyakorK]

🎩 Description

Try to fix initiatives based on the fix we made on the decidim-app with some slight changes

📌 Related Issues

• Fixes https://github.com/orgs/OpenSourcePolitics/projects/26/views/1?pane=issue&itemId=200919353&issue=OpenSourcePolitics%7Cintern-tasks%7C455

Testing

• Go to back-office
• Go to Initiatives and get one that is finished
• Try to export PDF and make sure it works

Tasks

• Add initializer
• Update Dockerfiles
• Update Gemfile and fix some dependencies does not work in local tho)
• Fix Postgres version on local docker-compose