OpenTelemetry - fix Span.kind property to return SpanKind instead of str

[przlada]

I found that the Span.kind property from the OpenTelemetry integration is returning a string value instead of a SpanKind enum. Because of this, the logic for setting the operation name cannot work properly

I propose to merge these changes as they:

• Fix the Span.kind property to return the SpanKind enum as it should, instead of a string value
• Thanks to this fix, the Span._datadog_operation_name property will start to work properly (as it is comparing to SpanKind enum values). I also fixed the logic for when the network.protocol.name attribute is set
• I added tests to validate that span names are properly set now, and updated some snapshot files

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[mabdinur]

Thanks for the fix!

Can you add a fix release note as well.

Here's the docs on how to generate and write a release note: https://github.com/DataDog/dd-trace-py/blob/main/docs/releasenotes.rst#generating-a-release-note.