Remove Alerting::Alert and AlertManagement::AlertParams

What does this MR do?

This refactor MR is a part of migrating interactions with alerts and their payloads to using Gitlab::AlertManagement::Payload subclasses.

Changes in this MR:

• Updates alert emails to reference attributes via AlertManagement::AlertPresenter instead of Gitlab::Alerting::Alert's presenter
• Transitions service for generic alert creation to use AlertManagement::Payload instead of Gitlab::AlertManagement::AlertParams
• Syncs up logic for payload-sizes & dynamic fingerprinting, descriptions, and end times in Gitlab::AlertManagement::Payload
• Removes now-obsolete classes & specs

This MR also makes Gitlab::Alerting::NotificationPayload::Parser nearly obsolete, but to keep this MR a little more manageable, I've done final cleanup & removal in !42527 (merged).

Related issues:

• #217407 (closed)
• #233450 (closed)
• #239029 (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

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