Create custom mapping for HTTP endpoints for alerts
### Release Notes
Managing integrations between tools in difficult, especially when you have several monitoring tools that alert on your services. Each of those has a unique alert format which means that you have to specifically modify those alerts to work with your incident management platform. Sending alerts to GitLab just got easier because now you can configure alert transformations for all of your tools in GitLab. Simply submit a sample payload for the tool by pasting it into GitLab and map fields from that payload to the attributes in GitLab's alert format.
Documentation: https://docs.gitlab.com/ee/operations/incident_management/alert_integrations.html
### Problem to solve
To set up an alert integration, a user needs to configure alerts from a monitoring tool to match the format accepted by an incident management application. Right now, users need to configure alerts in every monitoring tool that they use to match GitLab's alert format. Some monitoring tools do not allow customization of alert formats which that means, that right now they cannot integrate these tools into GitLab.
Adding the ability to create custom mappings between an external alert and GitLab's required alert format would allow the user to:
1. Consolidate all configuration required to integrate monitoring tools into one interface => GitLab
2. integrate tools that do not allow customization of alert payloads
### Intended users
* [Devon (DevOps Engineer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#devon-devops-engineer)
* [Allison (Application Ops)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#allison-application-ops)
### User experience goal
A user can paste in a sample payload of an alert with key:value pairs to GitLab. Clicking the submit button will parse the payload and load and create a custom mapping that will get saved with the associated HTTP endpoint.
### Proposal
Reuse the test alert input box for custom mapping functionality. A user will paste in a sample payload and submit it. GitLab will parse the payload into a flat list of keys and display them in the drop-down selectors under Payload alert keys. User can select
### Designs
| Mapping added to HTTP endpoint option | Dropdown options | Tooltip | Error | Final |
| ------ | ------ | ------ | ------ | ------ |
|  | |  | |  |
[Figma file](https://www.figma.com/file/ngP46IcxTj68Wwlmr8Jolq/Custom-integrations-gitlab-com-and-217766?node-id=351%3A16623)
### Further details
This work supports the [Incident Management](https://about.gitlab.com/direction/monitor/debugging_and_health/incident_management/) direction.
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