Add possibility to extend tracer options

[peterdeme]

What does this PR do?

Adding a possibility to extend the tracer options.

Motivation

We'd like to be able to extend the tracer with a couple of custom options.

Testing Guidelines

Additional Notes

Types of changes

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

Checklist

• [x] This PR's description is comprehensive
• [x] This PR contains breaking changes that are documented in the description
• [x] This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• [x] 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
• [x] This PR collects user input/sensitive content into Datadog

[peterdeme]

Thanks!