feat: Edge V2 migration opt-in, capacity budget for migration

[khvn26]

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Changes

Naming

IdentityOverridesV2MigrationStatus enumeration is renamed to EdgeV2MigrationStatus.

Settings

Added:

• EDGE_V2_MIGRATION_READ_CAPACITY_BUDGET: controls how much read capacity is allowed during migration to environments_v2. Default value is 0. The idea is to increase it to a sensible amount whenever Edge V2 is live.

Business logic

Renamed:

• Project.identity_overrides_v2_migration_status -> Project.edge_v2_migration_status.

Modified:

• DynamoIdentityWrapper.iter_all_items_paginated now accepts capacity_budget argument. If the budget is reached or exceeded during iteration, it raises a CapacityBudgetExceeded exception. If capacity_budget is 0, the error is raised before any request to DynamoDB is made.

Added:

• Project.edge_v2_read_capacity_budget overrides the EDGE_V2_MIGRATION_READ_CAPACITY_BUDGET for the given project. Field value is null by default.
• EdgeV2MigrationStatus.INCOMPLETE marks projects that have exceeded the read capacity budget during migration and have only environment documents migrated. Identity override migration is completely skipped for such projects.

API

• Added edge_v2_migration_status to project endpoints so the migration can be triggered via REST API.
• edge_v2_read_capacity_budget is only modifiable via Django admin page.

How did you test this code?

All code covered with unit tests.

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.17%. Comparing base (e8d1337) to head (031a0df).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3881      +/-   ##
==========================================
+ Coverage   96.01%   96.17%   +0.16%     
==========================================
  Files        1138     1141       +3     
  Lines       36443    36457      +14     
==========================================
+ Hits        34992    35064      +72     
+ Misses       1451     1393      -58     

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