docs(samples): add policyTagManager samples

[steffnay]

• [x] Ensure the tests and linter pass
• [x] Code coverage does not decrease (if any source code was changed)

• [x] Appropriate docs were updated (if necessary)

  🦕

[snippet-bot[bot]]

Here is the summary of changes.

You are about to add 5 region tags.

- [samples/policyTagManager/createPolicyTag.js:18](https://github.com/steffnay/nodejs-datacatalog/blob/fe5e720708bee5286057a7407d56060a9e26328a/samples/policyTagManager/createPolicyTag.js#L18), tag `data_catalog_ptm_create_policytag` - [samples/policyTagManager/createTaxonomy.js:18](https://github.com/steffnay/nodejs-datacatalog/blob/fe5e720708bee5286057a7407d56060a9e26328a/samples/policyTagManager/createTaxonomy.js#L18), tag `data_catalog_ptm_create_taxonomy` - [samples/policyTagManager/deleteTaxonomy.js:18](https://github.com/steffnay/nodejs-datacatalog/blob/fe5e720708bee5286057a7407d56060a9e26328a/samples/policyTagManager/deleteTaxonomy.js#L18), tag `data_catalog_ptm_delete_taxonomy` - [samples/policyTagManager/getTaxonomy.js:18](https://github.com/steffnay/nodejs-datacatalog/blob/fe5e720708bee5286057a7407d56060a9e26328a/samples/policyTagManager/getTaxonomy.js#L18), tag `data_catalog_ptm_get_taxonomy` - [samples/policyTagManager/listTaxonomies.js:18](https://github.com/steffnay/nodejs-datacatalog/blob/fe5e720708bee5286057a7407d56060a9e26328a/samples/policyTagManager/listTaxonomies.js#L18), tag `data_catalog_ptm_list_taxonomies`

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[gcf-merge-on-green[bot]]

Merge-on-green attempted to merge your PR for 6 hours, but it was not mergeable because either one of your required status checks failed, one of your required reviews was not approved, or there is a do not merge label. Learn more about your required status checks here: https://help.github.com/en/github/administering-a-repository/enabling-required-status-checks. You can remove and reapply the label to re-run the bot.

[tmatsuo]

FYI, Justin's merge commits make our CLA bot unhappy. You can omit them then force push to resolve it.

[steffnay]

closing in favor of https://github.com/googleapis/nodejs-datacatalog/pull/330