ORC-1185: Add merge_orc_pr.py
ORC-1185: Add merge_orc_pr.py

### What changes were proposed in this pull request?

This PR aims to add `merge_orc_pr.py` to help committers merge the PRs.

### Why are the changes needed?

This is borrowed from [Apache Spark community](https://github.com/apache/spark/blob/master/dev/merge_spark_pr.py) which provides several features like
- Supporting multi-author credits
- Cleaning up the PR template comments
- Landing on multiple branches
- Handling Apache JIRA during merging process

### How was this patch tested?

This should be tested manually after merging.

Closes #1136

Signed-off-by: Dongjoon Hyun <6ff48b33cbb828151035af58a92f18a39f1d1036@apache.org>

apache/orc,apache/orc,apache/orc,apache/orc,apache/orc,apache/orc,apache/orc,apache/orc