Header value doesn't update dynamically.

[jaanreinok]

The header value doesn't update. Layout value gets updated.
This would be useful in case of supplying metadata via header. The http target has BatchAsJsonArray="true" wrapped in BufferingWrapper.
custom layout render.
LayoutRenderer.Register("unixutcms", (logEvent) => DateTimeOffset.UtcNow.ToUnixTimeMilliseconds());

<header name="ClientUtcNowMs" value="${unixutcms}"/>
<layout type="JsonLayout" >
<attribute name="ts" layout="${unixutcms}" />
...

[DarekDan]

Relentless ... Layout renderers everywhere, huh? I will see what can be done, but no promises.