[Synthetics] Add support for Multi Step API journeys

[vigneshshanmugam]

Describe the feature:

Our Synthetics monitoring solution currently lacks the ability to do Multistep API journeys. The existing support relies on heartbeat yml HTTP monitors, lacking a scripting layer and if users would need to write them in a type-safe language like TypeScript and do multiple assertions. As we look towards improving our synthetics offering, enhancing support for Multistep API journeys with a more robust scripting capability becomes a key focus to meet the evolving needs of our users.

We need to do couple of things on the Kibana side and it should work on both Serverless and ESS cloud.

• Expose CRUD API for the new monitor.type api for running API based journey tests. This would be used as part of the npx @elastic/synthetics push command.
• Integration policies needs to be adjusted based on the datastream naming scheme for the new monitor type.
• Synthetics monitor UI
  • Add support for creating new monitor type during Create Monitor flow.
  • Account for the new monitor type including the Network Request waterfall and other step information. Missing information like traces, metrics, screenshots needs to be accounted for as this information will not be present for the apijourney monitor.
  • Remove screenshot_options under Advanced options in the Monitor Creation page.
  • Hide the Recorder flow till the recorder support is in place.

Describe a specific use case for the feature:

More details are on https://github.com/elastic/synthetics/issues/137 and https://github.com/elastic/synthetics/issues/900

[elasticmachine]

Pinging @elastic/obs-ux-management-team (Team:obs-ux-management)