Fixes HDX-3325
* Use enums where possible
* Add descriptions where missing
* Simplify Alert request and types
* Fix a disceprency with alert request and response fields: `team` vs `teamId`, `dashboard` vs `dashboardId`, `savedSearch` vs `savedSearchId`
Closes HDX-3303
# Summary
This PR reworks the external dashboard APIs in the following ways
1. Previously, there was no way to create a renderable dashboard using the create or update routes, because the APIs saved dashboard data in a format incompatible with v2 of HyperDX. This PR introduces a transformation layer to transform external API request and response formats into the v2 dashboard format prior to saving.
2. This PR also corrects and improves the openapi documentation associated with the dashboard endpoints.
This PR introduces a number of **breaking changes** in the dashboard API, which is acceptable because the APIs are already (a) effectively non-functional for writing dashboard data and (b) not aligned at all with the previously published spec when reading dashboard data.
1. The `dataSource` field has been removed from each series and replaced with a `sourceId` field, which specifies the sourceId of the source which should be queried. The `dataSource` argument was inflexible and could only specify `events`, `rrweb`, or `metrics` - these are leftover from V1, and are not very compatible with the design of HyperDX V2.
2. Dashboard responses previously would have contained `config` fields, in the format of a V2 dashboard config. Results are now transformed and align with the spec, which contains config data in a `series` array.
3. Additional validation has been added to prevent creation of some invalid dashboards
# Summary
This PR updates the external Alerts API specs so that the specs match the actual behavior of the API.
I've also added a validator to an API which was missing any validation.
