feat(action): add an output for the changelog content (#4)

* feat: add an output for the changelog content

::set-output is
[deprecated](https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/)
in favor of [environment
files](https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#environment-files).
This has better multiline support, so add the contents of the changelog as an output for cases where
you are creating a GitHub release.

BREAKING CHANGE: self-hosted runners will need to be at 2.297.0 or greater

* fix: update multiline output usage

https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#multiline-strings

* docs(readme): add content as output

Co-authored-by: Orhun Parmaksız <orhunparmaksiz@gmail.com>

entrypoint.sh

@@ -23,10 +23,15 @@ exit_code=$?
 
 # Output to console
 cat "$OUTPUT"
-OUTPUT="$WORKDIR/$OUTPUT"
+
+# Set the changelog content
+echo "content<<EOF" >> $GITHUB_OUTPUT
+cat "$OUTPUT" >> $GITHUB_OUTPUT
+echo "EOF" >> $GITHUB_OUTPUT
 
 # Set output file
-echo "::set-output name=changelog::$OUTPUT"
+OUTPUT="$WORKDIR/$OUTPUT"
+echo "changelog=$OUTPUT" >> $GITHUB_OUTPUT
 
 # Pass exit code to the next step
-echo "::set-output name=exit_code::$exit_code"
+echo "exit_code=$exit_code" >> $GITHUB_OUTPUT