Parse sample payload integration

What does this MR do?

Integrates parsing of sample alert payload with backend Here is the MR we're integrating with !53629 (merged)

Currently hidden behind multiple_http_integrations_custom_mapping feature flag

To check navigate to Operations=> Settings=>Expand Alert section or the direct link will be localhost/group/project/-/settings/operations#js-alert-management-settings

• Fill the form (make sure to select HTTP endpoint type on step 1)
• Toggle active
• Now you can paste and parse payload (any valid JSON) so that to configure alert mapping

Screenshots (strongly suggested)

Testing

Sample Payload

{
  "dashboardId":1,
  "evalMatches":[
    {
      "value":1,
      "metric":"Count",
      "tags":{}
    }
  ],
  "imageUrl":"https://grafana.com/static/assets/img/blog/mixed_styles.png",
  "message":"Notification Message",
  "orgId":1,
  "panelId":2,
  "ruleId":1,
  "ruleName":"Panel Title alert",
  "ruleUrl":"http://localhost:3000/d/hZ7BuVbWz/test-dashboard?fullscreen\u0026edit\u0026tab=alert\u0026panelId=2\u0026orgId=1",
  "state":"alerting",
  "tags":{
    "tag name":"tag value"
  },
  "title":"[Alerting] Panel Title alert"
}

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

Related to #262707 (closed)