docs(migration-guide): add migration guide

Author: dhanarab

docs/migration-guides/migration-guide-v0.69-to-v0.70.md

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+<a name="v0.70.0"></a>
+## [v0.70.0] - 2025-02-07
+
+### BREAKING CHANGE
+
+### AMS
+
+The following have been updated:
+
+- Model `net.accelbyte.sdk.api.ams.models.ApiInstanceTypeForNamespaceResponse` is renamed to `net.accelbyte.sdk.api.ams.models.ApiInstanceType`
+- Model `net.accelbyte.sdk.api.ams.models.ApiInstanceTypesForNamespaceResponse` is renamed to `net.accelbyte.sdk.api.ams.models.ApiInstanceTypesResponse`
+
+### Challenge
+
+- Operation `net.accelbyte.sdk.api.challenge.models.ModelCreateGoalRequest`
+    - field `Schedule` type is changed from `net.accelbyte.sdk.api.ams.models.ModelGoalSchedule` to `net.accelbyte.sdk.api.ams.models.ModelGoalScheduleRequest`
+- Operation `net.accelbyte.sdk.api.challenge.models.ModelUpdateGoalRequest`
+    - field `Schedule` type is changed from `net.accelbyte.sdk.api.ams.models.ModelGoalSchedule` to `net.accelbyte.sdk.api.ams.models.ModelGoalScheduleRequest`
+
+### GDPR
+
+- Operation `net.accelbyte.sdk.api.gdpr.operations.data_retrieval.AdminGeneratePersonalDataURL`
+    - parameter `password` is changed from required to optional.
+
+### IAM
+
+- Operation `net.accelbyte.sdk.api.gdpr.operations.data_retrieval.PublicUpgradeHeadlessWithCodeV4Forward`
+    - request body type changed from `AccountUpgradeHeadlessAccountWithVerificationCodeRequestV4 ` to `AccountUpgradeHeadlessAccountWithVerificationCodeForwardRequestV4`