docs: add some OTel attributes for DynamoDB spec

[david-luna]

This PR adds a couple of OTel attributes in DynamoDB instrumentation. These attributes are:

• table_names which is used in all commands affecting tables (putItem, deleteItem, updateItem, createTable, updateTable, deleteTable, ...)
• projection which is present in query and getItem commands

Having this information will be relevant to when analysing which table, and projection if applies, triggered the error or a slow execution.

May the instrumentation collect sensitive information, such as secrets or PII (ex. in headers)?

• Yes

  • Add a section to the spec how agents should apply sanitization (such as sanitize_field_names)

• No

  • Why? table names and query projection does not contain PII

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• If this spec adds a new dynamic config option, [add it to central config](https://github.com/elastic/apm/blob/main/specs/agents/configuration.md#adding-a-new-configuration-option).