chore(llmobs): add language tag to span events [backport 2.13]

[github-actions]

Backport b488c99 from #10681 to 2.13.

Adds a language:python tag to all LLMObs span events, to be used for internal analysis. No changelog needed since this isn't a user-facing functional change or fix (it will just show as an extra tag in the UI).

MLOB-1543

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

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: backport-10681-to-2.13
Commit report: 9220ba1
Test service: dd-trace-py

✅ 0 Failed, 955 Passed, 0 Skipped, 14m 37.11s Total Time

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-09-18 13:29:08

Comparing candidate commit 9220ba1 in PR branch backport-10681-to-2.13 with baseline commit eea8ed6 in branch 2.13.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 353 metrics, 47 unstable metrics.