Display feature, segment and segment override limits and prevent creation if exceeded

[matthewelwell]

We have added limits to the API to prevent the creation of features, segments and segment overrides above a certain limit for each project.

We should:

• Return those limits in the API response for projects, along with the current numbers of features, segments
• Return the total number of segment overrides on the response to get an environment
• Add the limits to the UI (perhaps as a warning banner when they are within 10% of their limit?)
• Prevent users from creating new entities when the limit is reached

As far as I can tell, this will involve adding the following fields to the API responses on the retrieve endpoints for project and environment:

# Project

max_segments_allowed
max_features_allowed
max_segment_overrides_allowed
total_segments
total_features

# Environment

total_segment_overrides

These can only be added to the retrieve endpoints, not the list endpoint, which will require a change to the FE that seemingly retrieves all the data from the list endpoints.

The warning banner should read:

"Your project|environment using X% of the total allowance of features|segments|segment overrides. Please contact support to discuss increasing this limit."

The limits are documented here.

The PR to add the limits is here.

Acceptance Criteria

• If number of features exceeds 90% of the limit, a warning banner is shown in the UI
• If number of features reaches limit, no features can be created through the dashboard
• If number of segments exceeds 90% of the limit, a warning banner is shown in the UI
• If number of segments reaches limit, no segments can be created through the dashboard
• If number of segment overrides exceeds 90% of the limit, a warning banner is shown in the UI
• If number of segment overrides reaches limit, no segments can be created through the dashboard