mimir-rules-action: set-output is deprecated (#4372)

* `mimir-rules-action`: `set-output` is deprecated

See https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

`set-output` will stop working on June 1st and is currently warning

* Update entrypoint.sh

* Correctly output multiline

Summary should use the multiline format: github/docs#21529

* Use `ENDOFSUMMARY` instead of EOF

operations/mimir-rules-action/entrypoint.sh

@@ -73,8 +73,10 @@ case "${ACTION}" in
 esac
 
 SINGLE_LINE_OUTPUT=$(echo "${OUTPUT}" | awk 'BEGIN { RS="%0A" } { gsub(/%/, "%25"); gsub(/\r/, "%0D"); gsub(/\n/, "%0A") } { print }')
-echo ::set-output name=detailed::"${SINGLE_LINE_OUTPUT}"
+echo "detailed=${SINGLE_LINE_OUTPUT}" >> $GITHUB_OUTPUT
 SUMMARY=$(echo "${OUTPUT}" | grep Summary)
-echo ::set-output name=summary::"${SUMMARY}"
+echo 'summary<<ENDOFSUMMARY' >> $GITHUB_OUTPUT
+echo "${SUMMARY}" >> $GITHUB_OUTPUT
+echo 'ENDOFSUMMARY' >> $GITHUB_OUTPUT
 
 exit $STATUS