Feat: add dataspace and iframe

[Stef-Rousset]

🎩 Description

This PR is linked to Multipod requirements.
It adds 2 functionalities:

• decidim-module-dataspace
• adds an iframe on the proposal show page

Testing

• For dataspace on local env, run

bundle install
bundle exec rake railties:install:migrations
bundle exec rake db:migrate
bundle exec rake comments:add_reference

1. Go to /system and enable dataspace
2. As an admin, go to the proposals component configuration page, check "Add integration" and provide a url like "http://localhost:3000"
3. As a user, go in the FO to the proposals index page, and see that proposals and external proposals are displayed (screenshot one)
4. Click on an external proposal card with comments, and see that the external proposal show page is displayed with comments.

• For iframe:

1. As an admin, go to the proposals component configuration page, check "Enable iframe" and provide a url like "https://api.multipod.weblyzard.com/embed/27kVzAqaTFRLZU9v6xBvtHyZcPeURpsg/lite/source=news%2Cnon-profit/topic=democracy/pills=elections%2Cpolicymaking/date=p-1m%2Cp0d" (screenshot two)
2. Go to /system, and in the advance settings add in frame src "api.multipod.weblyzard.com"
3. As a user, go in the FO to a proposal show page and see that the iframe is displayed (screenshot three)

Tasks

• Add specs
• In case of new dependencies or version bump, update related documentation

🛠️ If your PR introduces or updates an Override

• Add the label "override:pending" in your PR
• Add the corresponding label based on the review deadline category (when this override must be checked):
  • WHEN BACKPORT 0.29 ·
  • BEFORE MIGRATION 0.31 ·
  • WAITING FOR PR UPSTREAM ·
  • OTHER

📷 Screenshots

Please add screenshots of the changes you're proposing if related to the UI
ONE

TWO

THREE