Added script to sync fbcode changes with main branch (#4769)

* [WIP] Added script to sync fbcode changes with main branch

* Make unique branches for multiple runs of the script

* Updated the files

* Change echo message

* Addressed review comments

* Removed from_repo command line argument

* Make fork_main_branch optional

Author: prabhat00155

scripts/README.rst

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+Utility scripts
+===============
+
+* `fbcode_to_main_sync.sh`
+
+This shell script is used to synchronise internal changes with the main repository.
+
+To run this script:
+
+.. code:: bash
+
+    chmod +x fbcode_to_main_sync.sh
+    ./fbcode_to_main_sync.sh <commit_hash> <fork_name> <fork_main_branch>
+
+where
+
+``commit_hash`` represents the commit hash in fbsync branch from where we should start the sync.
+
+``fork_name`` is the name of the remote corresponding to your fork, you can check it by doing `"git remote -v"`.
+
+``fork_main_branch`` (optional) is the name of the main branch on your fork(default="main").
+
+This script will create PRs corresponding to the commits in fbsync. Please review these, add the [FBCode->GH] prefix on the title and publish them. Most importantly, add the [FBCode->GH] prefix at the beginning of the merge message as well.

scripts/fbcode_to_main_sync.sh

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+#!/bin/bash
+
+if [ -z $1 ]
+then
+    echo "Commit hash is required to be passed when running this script."
+    echo "./fbcode_to_main_sync.sh <commit_hash> <fork_name> <fork_main_branch>"
+    exit 1
+fi
+commit_hash=$1
+
+if [ -z $2 ]
+then
+    echo "Fork name is required to be passed when running this script."
+    echo "./fbcode_to_main_sync.sh <commit_hash> <fork_name> <fork_main_branch>"
+    exit 1
+fi
+fork_name=$2
+
+if [ -z $3 ]
+then
+    fork_main_branch="main"
+else
+    fork_main_branch=$3
+fi
+
+from_branch="fbsync"
+git stash
+git checkout $from_branch
+git pull
+# Add random prefix in the new branch name to keep it unique per run
+prefix=$RANDOM
+IFS='
+'
+for line in $(git log --pretty=oneline "$commit_hash"..HEAD)
+do
+    if [[ $line != *\[fbsync\]* ]]
+    then
+        echo "Parsing $line"
+        hash=$(echo $line | cut -f1 -d' ')
+        git checkout $fork_main_branch
+        git checkout -B cherrypick_${prefix}_${hash}
+        git cherry-pick -x "$hash"
+        git push $fork_name cherrypick_${prefix}_${hash}
+        git checkout $from_branch
+    fi
+done
+echo "Please review the PRs, add [FBCode->GH] prefix in the title and publish them."