Availability of Network Offering not taken into account in Web Interface

### problem

When loading the CreateIsolatedNetworkForm form, the availability is not taken into account in selecting the default network offering.
It seems the issue is also present in CreateSharedNetworkForm and CreateL2NetworkForm

### versions

Running 4.22.0 but issue still present in main branch

### The steps to reproduce the bug

1. Add network
2. Check if the pre-selected network is the one with Required availability

### What to do about it?

https://github.com/apache/cloudstack/blob/6dc259c7dab7bee0c4ff731271c61e2f2ee97532/ui/src/views/network/CreateIsolatedNetworkForm.vue#L565C1-L565C69
Change this line to select the first element with the availability "Required" instead of the first of the list (That is sorted by ID by default)

ui/src/views/network/CreateIsolatedNetworkForm.vue の 565 行目付近から始め、続いて CreateSharedNetworkForm と CreateL2NetworkForm の対応するデフォルト選択ロジックを調べます。Add network フローを再現し、事前選択される offering が、ID でソートされたリストの単純な先頭の offering ではなく、Required availability を持つ最初の offering であることを確認します。

索引モデルが issue の本文から書いたものです。