[ECT-4454][prometheus] Add documentation for V2 webhook

[josemallma-dd]

What does this PR do?

Updates the Prometheus integration README to document the V2 webhook endpoint for Alertmanager and improves the overall setup documentation with tabs, enhanced explanations, and better formatting.

Motivation

The Prometheus integration now supports a V2 webhook endpoint (event-management-intake.datadoghq.com/api/v2/events/webhook) that offers additional features compared to V1, including:

• Support for multiple query parameters (e.g., oncall_team for Datadog On-Call integration)
• Better integration with Datadog's event management system

This PR documents both webhook versions using tabs, with V2 as the preferred option. It also enhances the setup instructions by:

• Adding information about using Alertmanager matchers to route alerts to different receivers
• Including helpful tips about send_resolved configuration and its importance for On-Call page resolution
• Highlighting relevant configuration lines in code blocks
• Adding informational notes about group_by behavior
• Providing a link to the Prometheus Alertmanager section from the Events section for easier navigation

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[github-actions]

⚠️ Recommendation: Add qa/skip-qa label

This PR does not modify any files shipped with the agent.

To help streamline the release process, please consider adding the qa/skip-qa label if these changes do not require QA testing.

[cswatt]

Thanks for this PR! You're using the correct syntax for tabs in integration docs, but it's unexpectedly causing some bugs in rendering the code with the appropriate highlighted lines and indentations:

I've created DOCS-12839 to help fix this issue and for a general editorial review from the Docs team.

[drichards-87]

Looks like the issue with the tabs was fixed. I've left some additional (minor) feedback on the PR.

Review from drichards-87 is dismissed. Related teams and files:

• documentation
  • prometheus/README.md

[josemallma-dd]