GODRIVER-3314 Add PR Cherrypicker Task

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GODRIVER-3314

Summary

Make it easier to backport PRs by making the magic GitHub comment: drivers-pr-bot please backport to {target_branch}.

Background & Motivation

Less friction when backporting PRs to release branches.

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drivers-pr-bot please backport to master

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It looks like we missed something:

[2024/08/27 13:03:16.888] Running command 'shell.exec' in function 'fetch-source' (step 1.2 of 5) in block 'pre'.
[2024/08/27 13:03:16.898] bash: line 57: go: command not found
[2024/08/27 13:03:16.898] Command 'shell.exec' in function 'fetch-source' (step 1.2 of 5) in block 'pre' failed: shell script encountered problem: exit code 127.
[2024/08/27 13:03:16.898] Finished command 'shell.exec' in function 'fetch-source' (step 1.2 of 5) in block 'pre' in 10.005155ms.
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We do need the following: GO_DIST: "/opt/golang/go1.20"