Remove custom alert table formatting

What does this MR do?

Removes custom CSS that was used for the alert details table. This reduces technical debt and allows the alert detail table to be reused without having to copy CSS onto other pages.

This also applies sentence case to the alert data keys.

Changes:

• Use the normal table mode instead of the 'stacked' mode.
• Add fields prop to provide label styling.
• Add label formatting using our own humanize text util
• Remove custom CSS.

Issue: #248950 (closed)

To test:

1. Configure an alert endpoint (https://docs.gitlab.com/ee/operations/incident_management/#configure-external-generic-alerts).
2. Send an alert to the gitlab instance. (https://docs.gitlab.com/ee/operations/incident_management/generic_alerts.html#customizing-the-payload)
3. Navigate to the alerts list (Operations -> Alerts).
4. View the alert detail page by selecting one of the alerts.

Screenshots

before	after

Does this MR meet the acceptance criteria?

Conformity

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

Availability and Testing

• [n/a] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• [n/a] 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:

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