Optimise FE to remove N+1 calls to get project environments

Currently when landing on https://app.flagsmith.com/organisation/:organisationId/projects, the FE iterates over all the projects and requests the environments for each one. For organisations with large numbers of projects this causes a performance overhead at the very least, and rate-limiting at the worst.

The FE should not need to get the environments at this point in the load of the dashboard. The reason that it retrieves them is to know where to route the user to when selecting a project since the next URL is built as https://app.flagsmith.com/project/:projectId/environment/:environmentKey/features (by accessing `project.environments[0].api_key`.

Some possible solutions to this issue:

1. The API returns an `environments` list in each Project object returned on `/api/v1/projects`. The `environments` list could include:
a. The whole environment object
b. A summary object including the `id`, `api_key` and `name`
c. Just a list of strings giving the `api_key` attributes of the environments
2. The FE retrieves the environments when the user selects a project and then routes the user accordingly
3. The BE adds functionality to add a 'default_environment' attribute to the project which the FE can route to

Option (1) would likely be the easiest as it means no refactor on the FE. Option (3) is perhaps the cleanest, but opens the question about whether it would be better to store this preference per user, or maybe use something like `last_environment_visited`?