Initial version of x-org paging docs

[Dalje-et]

What does this PR do? What is the motivation?

Merge instructions

Merge readiness:

• Ready for merge

For Datadog employees:

Your branch name MUST follow the <name>/<description> convention and include the forward slash (/). Without this format, your pull request will not pass CI, the GitLab pipeline will not run, and you won't get a branch preview. Getting a branch preview makes it easier for us to check any issues with your PR, such as broken links.

If your branch doesn't follow this format, rename it or create a new branch and PR.

[6/5/2025] Merge queue has been disabled on the documentation repo. If you have write access to the repo, the PR has been reviewed by a Documentation team member, and all of the required checks have passed, you can use the Squash and Merge button to merge the PR. If you don't have write access, or you need help, reach out in the #documentation channel in Slack.

Additional notes

[github-actions]

✅ Documentation Team Review

The documentation team has approved this pull request. Thank you for your contribution!

[drichards-87]

@Dalje-et Is this PR related to #30985?

[github-actions]

Preview links (active after the build_preview check completes)

New or renamed files

• https://docs-staging.datadoghq.com/daljeet/x-org-paging/service_management/on-call/cross_org_paging

[drichards-87]

Created DOCS-11771 for Docs Team review.

[cswatt]

I pushed some changes:

• We love having a "why you should use this" segment on pages like this. Usually there's not enough motivation-related content, but this time, there was maybe too much of it (the same sentiment was repeated a few times) and verged into marketing-sounding territory. I edited this down.
• Renamed headings and restructured sections to align with the format and conventions of other documentation pages (for example, "How it works" is typically the heading for a section that explains the under-the-hood workings of a feature, not for a setup/config flow)
• Consolidated setup steps into a numbered list.
• Added a "get an API key" step, since users need to supply a destination org API key when creating a connection.
• Added more explicit instructions around connection creation.
• Added links
• Various minor style/grammar edits