Bump GCP resource detector to latest

[xrmx]

What does this pull request do?

Bump GCP resource detector so we can drop our own entry point.

Related issues

[github-actions]

🔍 Preview links for changed docs

• docs/reference/edot-python/configuration.md

[github-actions]

✅ Vale Linting Results

No issues found on modified lines!

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Enterprise

Run ID: ccdac0ea-11d0-4b2e-afe8-5dca3216371b

📥 Commits

Reviewing files that changed from the base of the PR and between 0e3fd4a and f7bac6b.

📒 Files selected for processing (3)

• dev-requirements.txt
• pyproject.toml
• tests/distro/test_distro.py

✅ Files skipped from review due to trivial changes (2)

• tests/distro/test_distro.py
• dev-requirements.txt

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📝 Walkthrough

Walkthrough

This PR upgrades the OpenTelemetry GCP resource detector library from version 1.8.0a0 to 1.12.0a0 and replaces the internal placeholder identifier _gcp with the new official gcp_resource_detector throughout the codebase. The entry-point in pyproject.toml that mapped _gcp is removed, detector constants are updated with the new name, and all corresponding tests and documentation are adjusted to match.

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch bump-gcp-resourcedetector

• 🛠️ Update Documentation

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Actionable comments posted: 1

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Enterprise

Run ID: 886f4ad5-4dcf-4fe7-afa8-cdb65ecae3fa

📥 Commits

Reviewing files that changed from the base of the PR and between c44bd8b and 0e3fd4a.

📒 Files selected for processing (6)

• dev-requirements.txt
• docs/reference/edot-python/configuration.md
• pyproject.toml
• src/elasticotel/distro/resource_detectors.py
• tests/distro/test_distro.py
• tests/distro/test_resource_detectors.py