feat: Added node sample codes for cloud-iot-token-service generateAccessToken API

[codepriestz]

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Fixes #<issue_number_goes_here> 🦕

[snippet-bot]

Here is the summary of changes.

You are about to add 5 region tags.

• samples/access_token_example/access_token.js:31, tag iot_generate_access_token
• samples/access_token_example/access_token.js:79, tag iot_access_token_pubsub
• samples/access_token_example/access_token.js:174, tag iot_access_token_gcs
• samples/access_token_example/access_token.js:292, tag iot_access_token_service_account_token
• samples/access_token_example/access_token.js:333, tag iot_access_token_iot_send_command

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