ios: add ability to override SDK version when releasing

ios/scripts/release-sdk.sh

 THIS_DIR=$(cd -P "$(dirname "$(readlink "${BASH_SOURCE[0]}" || echo "${BASH_SOURCE[0]}")")" && pwd)
 PROJECT_REPO=$(realpath ${THIS_DIR}/../..)
 RELEASE_REPO=$(realpath ${THIS_DIR}/../../../jitsi-meet-ios-sdk-releases)
-SDK_VERSION=$(/usr/libexec/PlistBuddy -c "Print CFBundleShortVersionString" ${THIS_DIR}/../sdk/src/Info.plist)
+DEFAULT_SDK_VERSION=$(/usr/libexec/PlistBuddy -c "Print CFBundleShortVersionString" ${THIS_DIR}/../sdk/src/Info.plist)
+SDK_VERSION=${OVERRIDE_SDK_VERSION:-${DEFAULT_SDK_VERSION}}
 
 
 echo "Releasing Jitsi Meet SDK ${SDK_VERSION}"