Adding Observability CSP Concern to relevant controllers

What does this MR do and why?

This is a companion MR to !104081 (merged)

In order for us to be able to embed Observability iframe into different parts of GitLab (i.e. issues, MRs, epics - wherever content editor is present ) we need to add the Observability URL in the frame-src CSP policy.

This MR enables such CSP policy for Issues, MR and Epics controller.

This is easily done (and tested) with the recently added (MR) Observability::ContentSecurityPolicy and RSpec.shared_examples 'observability csp policy'

Screenshots or screen recordings

N/A

How to set up and validate locally

• https://gitlab.com/gitlab-org/opstrace/opstrace-ui/-/blob/main/contribute/developer-guide.md#run-gitlab-observability-ui-with-local-gdk
• Run rspecs

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.