[New feature] Comma separated list syntax for HX-Trigger response header

[Telroshan]

Adds support for comma separated list of event names to the HX-Trigger response header. Currently, to trigger multiple events with that header, you have to use the JSON syntax, even if you don't have any additional data to send.

This change lets you specify a list of event names, separated by commas, without additional details, like so: HX-Trigger: event1, event2

The syntax is similar to the one of the hx-target attribute, that also supports a comma separated list syntax