Epic: V2 API

This is expected to be a long running ticket where we can list breaking changes that we want to include in a V2 API. As part of this work, we should plan the new API interface around the key journeys that customers need to use our REST API for to simplify admin integrations.

- Add consistent API interface across all Edge endpoints. These should all respond with a consistent schema that follows a well defined framework, e.g. https://jsonapi.org/.
- specifically, this will allow us to remove the 'updated at' value from the header of the `/flags/` endpoint and into the response body
- Look into fixing the typing issues. All dynamically typed fields should be removed and replaced with a combination of a string field and a provided data type.
- Replace all references to 'unicode' with 'string'
- Create endpoints to manage state of a feature for an environment, identity or segment without needing to make multiple API requests
- Prevent updates to FeatureState objects - we should only allow new versions to be created
- Remove endpoints reliant on influx data in favour of endpoints that return data from influx or postgres for analytics purposes
- Update authentication such that it includes context of the organisation for each request
- Remove integration configuration objects from environment-document endpoint
- Remove dynatrace configuration from the engine / edge api entirely
- Remove need for FeatureSegment
- Remove `"description"` field from environment list endpoint (see discussion [here](https://github.com/Flagsmith/flagsmith/pull/2947/files#r1388331387) for reference)