Docs/openapi spec for alert configs (#94)

* docs: Add `AlertConfig` schema to OpenAPI spec

* docs: Add `Alert Configurations` tag to OpenAPI spec

* docs: Add endpoints for listing and creating alert configurations to OpenAPI spec

* docs: Add `AlertConfigSummary` schema and use for listing alert configs

* docs: Add endpoints for working on specific alert configurations

* docs: Add endpoints for working with alert configs and monitors

* docs: Fix description for endpoint that deletes a Monitor

* docs: Group Monitors x Alert config endpoints together

* chore: Remove superfluous double-quotes from OpenAPI spec

* docs: Update the main description for the API in the OpenAPI spec