ensure tracer initialization does not override DD_TAGS

[wconti27]

What does this PR do?

Prevents DD_TAGS from being overwritten.

Motivation

Customer escalation

Testing Guidelines

Additional Notes

Types of Changes

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

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• [ ] 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)
• [ ] This PR's changes are covered by the automated tests
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• [ ] This PR passes the integration tests (ask a Datadog member to run the tests)