[SPARK-52964] Add merge_connect_rust_pr.py and PULL_REQUEST_TEMPLATE (#3)

This PR proposes adding merge_connect_rust_pr.py and PULL_REQUEST_TEMPLATE like the Spark repository does.
These files are brought from Spark repository and tweaked.

Author: sarutak

.github/PULL_REQUEST_TEMPLATE

@@ -0,0 +1,54 @@
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