Show identity overrides pagination warning

[khvn26]

Currently, when /api/v1/environment-document starts serving paginated responses due to total overrides exceeding the 1MB response size limit, there's no way for the user to find out unless they notice missing overrides during local evaluation.

This will be the case for quite some time until all the server SDKs are updated to support pagination.

For now, we should check for additional pages and add a UI warning in the Environment context saying the following text:

Environment <environment> has reached an Identity overrides in Local Evaluation mode limit. Some of the overrides will not work in Local Evaluation mode. Turn off Local Evaluation mode for the SDKs that use it or remove unneeded identity overrides.

Use the logic below to determine whether the banner should be shown:

[matthewelwell]

Related to #4664

[matthewelwell]

As discussed with @khvn26 , this isn't as simple as just getting the UI to display a warning, because the UI doesn't have access to a server key needed to retrieve the environment document and determine if the LINK header is there.

We'll need to implement something in the API to provide this information to the UI.

[matthewelwell]

@khvn26 does the EnvironmentViewSet.get_document return the same header?

[jasonw-rr]

@matthewelwell
Can we display this warning on admin UI or display as usage on Flagsmith's setting page instead?
https://app.flagsmith.com/project/{porject_id}/settings?tab=usage

At least it's more obvious to troubleshoot for engineers or flag managers

[matthewelwell]

@jasonw-rr sorry, I'm not sure what you mean by 'instead' ? Our intention is to display this warning in the admin UI, yes.

[jasonw-rr]

@matthewelwell
Sorry, I got confused with the responses. (I thought you meant public client without server key)
Scratch my previous message.

We can access to server-side environment key via Admin UI, why can't we use it to get /api/v1/environment-document?