Implement transaction_name_groups config

[felixbarny]

The Node.js agent supports the usePathAsTransactionName option.

A risk of using this option is that it can lead to cardinality issues when the path contains parameters. To mitigate this, the Node.js agent should

• Implement the transaction_name_groups option
• Add a warning to the usePathAsTransactionName docs, similar to the one from the Java agent.