build(node): update client library version in samples metadata (#1356) (#618)

* build(node): add feat in node post-processor to add client library version number in snippet metadata

Co-authored-by: Benjamin E. Coe <[email protected]>
Source-Link: googleapis/synthtool@d337b88
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-nodejs:latest@sha256:d106724ad2a96daa1b8d88de101ba50bdb30b8df62ffa0aa2b451d93b4556641

Author: gcf-owl-bot[bot]