Update CODEOWNERS with new team structure

[Copilot]

Updates CODEOWNERS to reflect team reorganization and establish shared ownership.

Changes

• Renamed @elastic/security-scalability to @elastic/integration-experience
• Added @elastic/security-service-integrations as co-owner

Both teams now share ownership of all files in the repository.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Update codeowners file with new team definition</issue_title>
<issue_description>## Description
The goal is to have shared code ownership for this repository between integration-experience and service-integrations

Tasks

1. rename @elastic/security-scalability to @elastic/integration-experience as this is the new combined team
2. add co-ownership to @elastic/security-service-integrations </issue_description>

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

• Fixes Update codeowners file with new team definition #75

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.