Is your feature request related to a problem? Please describe.
currently extensions can be either already published GAV's or a directory of jars - it would be great to use have ability to use jbang scripts/apps which could be built on-demand.

Describe the solution you'd like

refer to source files

extensions:
  github-summary:
    jbang: src/jreleaser/extensions/myext.java

extensions:
  github-summary:
    jbang: src/jreleaser/extensions/myext.kt

and even remote jbang script refs:

extensions:
  github-summary:
    jbang: https://gist.github.com/maxandersen/a9486a710dbdea5e65066909171ef4f8