feat: [SVLS-5765] use DD_BOTOCORE_ADD_SPAN_POINTERS

[apiarian-datadog]

What does this PR do?

Respect the DD_BOTOCORE_ADD_SPAN_POINTERS environment variable that is also used by dd-trace-py to opt out of automatic botocore span pointers.

Testing Guidelines

Unit tests. Also confirmed that this works as expected in a live test lambda setup.

Types of Changes

• [ ] Bug fix
• [x] New feature
• [ ] Breaking change
• [ ] Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• [x] This PR's description is comprehensive
• [ ] This PR contains breaking changes that are documented in the description
• [ ] This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• [ ] This PR impacts documentation, and it has been updated (or a ticket has been logged)
• [x] This PR's changes are covered by the automated tests
• [ ] This PR collects user input/sensitive content into Datadog
• [x] This PR passes the integration tests (ask a Datadog member to run the tests)