Add support for HTMX attribute hx-include

[henhuy]

In my project, I trigger HTMX from a single button (which is not included in any form) and include form inputs from multiple other forms by using HTMX attribute hx-include (see in HTMX doc: https://htmx.org/attributes/hx-include/).

I will add a PR which tries to solve this issue...

[benopotamus]

This appears to be working in htmx 2.0 without any coercing by this shoelace extension 🥳