Add table to store Alert Management Alerts

What does this MR do?

This adds a table to store the AlertManagement::Alerts for the the Alert Management epic.

Table structure has been discussed prior to implementation in #214518 (closed).

Screenshots

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 #214518 (closed)