Add Migration guide

MIGRATION.md

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+# Migration Guide
+
+## Upgrading from 3.x to 4.0
+
+### Core Resources
+
+- Applicants
+  - Replace broken `ConsentsBuilder` object with a list of `ApplicantConsentBuilder` ones
+- Workflow Runs
+  - Rename `WorkflowRunSharedLink` object into `WorkflowRunLink`
+  - Define `WorkflowRunStatus` enum for storing status information
+  - Rename `WorkflowRunResponseError` object into `WorkflowRunError`
+- Documents
+  - Reuse already existent `DocumentTypes` enum when uploading documents
+
+### Other Endpoints
+
+- Webhooks
+  - Define `WebhookEventObjectStatus` enum to collect webhook event object's status
+  - Define `WebhookEventResourceType` enum to collect webhhok event resource's type
+  - Define `WebhookEventPayloadResource` object to store webhook payload's contents
+- Checks
+  - Define `CheckStatus` enum for accessing checks status
+- Reports
+  - Remove properties from `DeviceIntelligenceBreakdownPropertiesDevice` object: `true_os`, `os_anomaly`, `rooted` and `remote_software`
+  - Remove properties from `DeviceIntelligenceBreakdownPropertiesIp` object: `vpn_detection`, `proxy_detection` and `type`
+
+### OpenAPI generator
+
+- Version upgraded from 7.6.0 to 7.9.0