WIP: Cleanup AlertsService usage for generic alerts

What does this MR do?

• Remove alerts service from initialization request from project Setting > Operations > Alerts (except for as required for OpsGenie)
• Ensures Operations > Alerts is viewable if there are active alerts, even if the alerting services have been disabled
• Allows self-monitoring of ~"group::monitor" projects to use HTTP integrations instead of the older AlertsService integrations (all AlertsServices were migrated to HttpIntegrations, so they'll still exist for the relevant projects)
• Allows Prometheus alerts sent to an HTTP endpoint to still be processed as a prometheus alert
• Unrequire incident titles to come from the generic alerts service in order to include the incident iid
• Remove #alerts_service_activated? helper

Screenshots (strongly suggested)

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

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