Add option to provide message context (metadata) to the start/end/info-points

[nielsm5]

See wearefrank/ladybug-frontend#458

There was no issue on this project board, we at the Frank!Framework are still looking for a way to add more metadata to the messages.

When using an info, start of end-point we like to be able to provide more information about the message, such as the charset, size, location (if known), mimetype (when known), http headers etc.