feat: Allow gitlab agent to create alert

What does this MR do?

This MR creates internal end point for KAS server to create an alert trough new service. As first iteration, alerts that are created trough this channel won't have side effects like creating issues automatically etc. End point will accept payload same as alert integration

Related issues

#277149 (closed)

Does this MR meet the acceptance criteria?

Steps to reproduce

• Follow provided doc and create agent record
• Following doc make api request to <your_instance>//internal/kubernetes/network_alert , with "{ title":"title", "description":"description" } payload.
• You should be able to see alert created in operations -> alert view

Screenshot

Conformity

• Changelog entry
• Code review guidelines
• Style guides

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team