Update install-agent.sh script in Azure Cloud Asset Inventory ARM Template to handle --install-servers flag

**Motivation**

Cloud Asset Inventory integrations for both 8.x and 9.x versions reference the same install-agent.sh script on the main branch. Since there is a breaking change in version 9.x, we need to add the --install-servers flag to properly handle Cloudbeat installation on the Elastic Agent. To accommodate this, the script should include a version check and adjust the installation command accordingly based on the provided version.

**Definition of done**
- [ ] install-agent.sh script is updated and working as expected

**Related Tasks**
- https://github.com/elastic/security-team/issues/11500