Sorting for Alert Management Alerts in GraphQL

What does this MR do?

This adds sorting for the AlertManagement::Alerts via the GraphQL API.

To do this we have added sorting scopes to the model, which call be called through the finder.

The following fields are able to be sorted on:

• Severity
• Start time
• End time
• Events
• Status

Also (via the Sortable module):

• ID
• Created at
• Updated at

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Related to #215598 (closed)