Add Datadog Agent instructions

[ramonguiu]

Description

[Short summary of why you created this PR]

Links

Fixes #[insert issue link, if any]

Writing help

For information about style and word usage, see the style guide

Review checklists

Reviewers: use this section to ensure you have checked everything before approving this PR:

Subject matter expert (SME) review checklist

• [ ] Is the content technically accurate?
• [ ] Is the content complete?
• [ ] Is the content presented in a logical order?
• [ ] Does the content use appropriate names for features and products?
• [ ] Does the content provide relevant links to further information?

Documentation team review checklist

• [ ] Is the content free from typos?
• [ ] Does the content use plain English?
• [ ] Does the content contain clear sections for concepts, tasks, and references?
• [ ] Have any images been uploaded to the correct location, and are resolvable?
• [ ] If the page index was updated, are redirects required and have they been implemented?
• [ ] Have you checked the built version of this content?

[github-actions[bot]]

Allow 10 minutes from last push for the staging site to build. If the link doesn't work, try using incognito mode instead. For internal reviewers, check web-documentation repo actions for staging build status. Link to build for this PR: http://docs-dev.timescale.com/docs-datadog-agent

[github-actions[bot]]

Oh no, the docs build failed! To see why visit the failing build (link only accessible to Timescalers).

[billy-the-fish]

@ramonguiu , we had build issues for this PR, it has been moved to https://github.com/timescale/docs/pull/4025#pullrequestreview-2771552241. You can see the docs https://docs-dev.timescale.com/docs-datadog-agent-integration/integrations/datadog-agent-integration/datadog/#configure-datadog-agent-to-collect-metrics-for-your-timescale-cloud-services.