Load youtube embeds lazily

go/blog/blog.go

<article id="{{ .Id }}" class="{{ .Type }}" {{- if .Tags }} data-tags="{{ json .Tags }}"{{ end }}>
	{{- template "title" . }}
	{{ if (eq .Provider "youtube" "vimeo") -}}
	<iframe width="560" height="315" src="{{ safe_url .URL }}" frameborder="0" allowfullscreen></iframe>
	<iframe width="560" height="315" src="{{ safe_url .URL }}" frameborder="0" allowfullscreen loading="lazy"></iframe>
	{{- else if (eq .Provider "native") -}}
	<video src="{{ safe_url .URL }}" controls></video>
	{{- end }}