Add ContentType header to metadata code snippets
Add ContentType header to metadata code snippets

Lack of this header causes the code snippets to fail (eg: in PHP)
hamzawi06/docs,auth0/docs,Annyv2/docs,auth0/docs,jeffreylees/docs,sandrinodimattia/docs,auth0/docs,hamzawi06/docs,sandrinodimattia/docs,yvonnewilson/docs,jeffreylees/docs,Annyv2/docs,sandrinodimattia/docs,khorne3/docs,yvonnewilson/docs,jeffreylees/docs,hamzawi06/docs,khorne3/docs,yvonnewilson/docs,khorne3/docs,Annyv2/docs