Fix product-ei/issues/2220

[indikasampath2000]

Purpose

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Durable subscription failed to connect after database recovery fixed with this PR. This is a race condition that came with MSSQL. We found that clusterNotificationAgent#notifySubscriptionsChange doing some database in the subscriber close event. So moved it to if (!storeUnavailable). For the safer side, move storageQueue#unbindSubscription to the same block because we use RDBMS based coordination.

Resolves: https://github.com/wso2/product-ei/issues/2220

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