Only admins of org could access to /petitions/manage

[markets]

Closes #782

[Copilot]

Pull Request Overview

This pull request restricts access to the petitions management functionality so that only organization admins (or superadmins) can perform manage actions. Key changes include:

• Addition of a manage? method in PetitionPolicy with admin authorization logic.
• Updates to the petitions_controller to enforce authorization in the update and manage actions.
• New test cases for admin versus non-admin access in petitions_controller_spec.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
app/policies/petition_policy.rb	Adds manage? and update? methods; potential bug in variable usage in manage?
spec/controllers/petitions_controller_spec.rb	Adds tests to check that only admins can access the manage action
app/controllers/petitions_controller.rb	Enforces authorization in update and manage actions

[markets]

@franpb14 @sseerrggii Going to merge this one too, already tested locally and by a new test case ✔️

Next: review all relevant changes we have in develop (Bootstrap and Rails upgrades and this one), in staging. But we need to fix the Docker build (#786) first.