Metatag og:image in country and measurement pages

[kronaemmanuel]

This PR includes the commits for og:image in country and measurement pages.

Screenshots

• Country Page
• Measurement Page:

[sarathms]

• [ ] prefetch just occurred as a passing thought. adding this here just in case I forget to mention it later when this PR is ready for formal review

[hellais]

Next steps:

• We are going to drop the flags from the screenshots
• Check the performance of puppeteer
• TODO(@kronaemmanuel) Disable the API endpoints for screenshotting prior to merge and ensure the attack surface is not increased
• Before re-enabling API endpoints we should have done a security audit of the code
• TODO(@hellais): Finalise the mockups for the country page screenshot without the country flag & also for the measurement page without the flag

[hellais]

Final mockup for the country page screenshot: