Add Incident Response to billing docs

[amlakhanpal]

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]

Preview links (active after the build_preview check completes)

New or renamed files

• https://docs-staging.datadoghq.com/amlakhanpal/incident-response-billing/account_management/billing/incident_response

[aflinois]

Edits suggeted:

"Each product bills by seat, meaning every user who performs qualifying actions requires a seat license. For detailed pricing information, see the Incident Response pricing page."

in the "What is a seat?" section can we bold some of the words like on-call seat, incident management seat and incident response seat?

"Claiming a Seaet" --> typo to fix

"How Billing Works" --> can we add what happens when

• a user claims a seat in a give month --> the seat is charged M2M forever until it is removed
• a user is removed in a given month --> the seat is still charged that month but not the following month