ddtrace/opentelemetry: Fix http remapping to account for int values

[zarirhamza]

What does this PR do?

Changes code due to the unforeseen circumstance that otel values for http.response.status_code are int values while Datadog uses http.status_code as a string value

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

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