eng, set default node version to 18.15.0 (#38135)

* set default node version to 18.15.0

* revert change on sdk_init.sh

* Update init.sh

Author: haolingdong-msft

eng/mgmt/automation/init.sh

@@ -4,6 +4,12 @@ sudo apt-get install -y --upgrade python3-pip python3-setuptools
 pip3 install --upgrade wheel
 pip3 install --upgrade PyYAML requests
 
+curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.3/install.sh | bash
+export NVM_DIR="$HOME/.nvm"
+[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh" # This loads nvm
+nvm install v18.15.0
+nvm alias default node
+
 cat << EOF > $2
 {"envs": {"PATH": "$JAVA_HOME_11_X64/bin:$PATH", "JAVA_HOME": "$JAVA_HOME_11_X64"}}
-EOF
+EOF