docs(nodejs_mono_repo): update broken links in README

[sofisl]

Makes sure file names do not contain /workspace/google-cloud-node/, since the post-processor runs from the root, but the link only needs the relative directory.

Since this is a shared function, we need to make the changes in the node post-processing.

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• tests/fixtures/nodejs_mono_repo_with_samples/packages/datastore/samples/workspace/google-cloud-node/random_sample.js:24, tag metastore_v1_generated_DataprocMetastore_CreateBackup_async

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