feat: support sending metrics before handler initialization

[duncanista]

What does this PR do?

Allows customer to use the API sendDistributionMetric and sendDistributionMetricWithDate outside of the handler.

Motivation

515

Testing Guidelines

• Added unit tests
• Added integration test
• Tested manually

Additional Notes

SVLS-4633

Types of Changes

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

Check all that apply

• [ ] 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
• [ ] This PR collects user input/sensitive content into Datadog
• [ ] This PR passes the integration tests (ask a Datadog member to run the tests)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 81.39535% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 81.89%. Comparing base (dadad52) to head (5b2885d).

:exclamation: Current head 5b2885d differs from pull request most recent head 59d713d. Consider uploading reports for the commit 59d713d to get more accurate results

Files	Patch %	Lines
src/index.ts	60.00%	6 Missing :warning:
src/utils/log.ts	60.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #524 +/- ## ========================================== + Coverage 81.75% 81.89% +0.13% ========================================== Files 54 55 +1 Lines 2209 2248 +39 Branches 515 519 +4 ========================================== + Hits 1806 1841 +35 - Misses 337 343 +6 + Partials 66 64 -2 ```

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