feat: add missing security header

[ilayda-cp]

Done

• Added wildcard to the img-src as it throws error when it tries to fetch an image from https://www.google.*/ads/ga-audiences

How to QA

• go to HTTP header analyzer
• verify all the security headers exist.
• go to https://charmhub-io-1997.demos.haus/
• Verify all the resources are shown correctly
• Verify there is no behavior change (such as a link doesnt open)
• Go to https://charmhub-io-1997.demos.haus/postgresql/docs/r-all-releases
• Verify green ticks are shown
• Go to https://charmhub-io-1997.demos.haus/traefik-k8s/docs/tls-termination
• Verify the images are shown

Testing

• This PR has tests
• No testing required (explain why): added csp

Issue / Card

Fixes #14416

[webteam-app]

Demo

Jenkins

demos.haus

[steverydz]

LGTM 👍

[chillkang]

LGTM👍