Add Google's 'no image preview' meta tag to organisation index pages

[AshGDS]

What

• Adds Google's max-image-snippet meta tag to each organisation's index page. The meta tag's value is set to the value none, which should prevent a featured image showing up next to organisation pages on Google Search results.

Why

• Google seems to be showing some of our organisation pages as "Rich snippets". In other words, it's adding an image from the organisation page next to the search result.
• From looking online, it seems that Google decide themselves what image from the page they think is best to feature next to a search result.
• This may be a problem for us due to some examples we've been alerted to. It seems that for some organisations they are taking a photo of someone in the "Related people" section, and using them as the featured image on Google. This may cause concern due to interpretations that can be made by having a person as the featured image for a whole organisation. As well as this, sometimes it grabs one of the Featured images, which could also be an issue depending on what the featured image is.
• You can stop Google from showing an image preview on a search result with the max-image-snippet meta tag. Therefore I've added it in this PR.

Affected search results

• https://www.google.com/search?q=Prime+Minister%27s+Office%2C+10+Downing+Street
• https://www.google.com/search?q=Attorney%20General%27s%20Office
• https://www.google.com/search?q=Cabinet+Office
• https://www.google.com/search?q=Department+for+Culture%2C+Media+%26+Sport
• https://www.google.com/search?q=department+for+environment+food+%26+rural+affairs
• https://www.google.com/search?q=Department+for+Science%2C+Innovation+%26+Technology
• https://www.google.com/search?q=Department+for+Transport
• https://www.google.com/search?q=FCDO
• https://www.google.com/search?q=Foreign%2C+Commonwealth+%26+Development+Office
• https://www.google.com/search?q=HM+Treasury
• https://www.google.com/search?q=Ministry%20of%20Defence
• https://www.google.com/search?q=Office%20of%20the%20Advocate%20General%20for%20Scotland
• https://www.google.com/search?q=Office%20of%20the%20Secretary%20of%20State%20for%20Scotland
• https://www.google.com/search?q=Office%20of%20the%20Secretary%20of%20State%20for%20Wales
• https://www.google.com/search?q=Forestry%20Commission

[AshGDS]

Thanks @maxgds