docs: Update README examples from v1 to v2

[Copilot]

v2 added support for the latest Node.js runtime available in GitHub Actions. README examples still referenced v1, misleading new users away from the current release.

Changes

• masci/datadog references: Updated all 5 occurrences of masci/datadog@v1 → masci/datadog@v2 across all usage examples (metrics, events, service checks, logs, and inputs reference)
• actions/checkout references: Updated 3 occurrences of actions/checkout@v2 → actions/checkout@v4 in examples that include a checkout step
• Warning note: Updated the suggested pinned version tag example from @v1 to @v2

Original prompt

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This section details on the original issue you should resolve

<issue_title>[docs] Update the README to use v2 in the examples.</issue_title>
<issue_description>Now that v2 was released with support for the latest version of node.js available in Github actions, we should update the README.md file to showcase the use of the latest version of the project</issue_description>

<agent_instructions>Work on this task</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@masci @copilot work on this

• Fixes [docs] Update the README to use v2 in the examples. #54

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[Copilot]

Pull request overview

Updates README examples to reference the current v2 release of the masci/datadog action, and bumps actions/checkout references to v4, matching what's currently available.

Changes:

• Updated all masci/datadog@v1 → masci/datadog@v2 references across usage examples
• Updated actions/checkout@v2 → actions/checkout@v4 in example workflows
• Updated the warning note's suggested pinned version tag from @v1 to @v2

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