docs: add docs for checksums migration (cosmos#5335)

* docs: add docs for checksums migration

* linting

docs/docs/03-light-clients/04-wasm/09-migrations.md

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+---
+title: Migrations
+sidebar_label: Migrations
+sidebar_position: 9
+slug: /ibc/light-clients/wasm/migrations
+---
+
+# Migrations
+
+This guide provides instructions for migrating 08-wasm versions.
+
+## From ibc-go v7.3.x to ibc-go v8.0.x
+
+## Chains
+
+In the 08-wasm versions compatible with ibc-go v7.3.x and above from the v7 release line, the checksums of the uploaded Wasm bytecodes are all stored under a single key. From ibc-go v8.0.x the checksums are stored using [`collections.KeySet`](https://docs.cosmos.network/v0.50/build/packages/collections#keyset), whose full functionality became available in Cosmos SDK v0.50. There is therefore an [automatic migration handler](https://github.com/cosmos/ibc-go/blob/51469420d8b14021768eacf0d8a61c5036a7eb91/modules/light-clients/08-wasm/module.go#L115-L118) configured in the 08-wasm module to migrate the stored checksums to `collections.KeySet`.