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)

Start at ui/src/views/network/CreateIsolatedNetworkForm.vue around line 565, then inspect the corresponding default-selection logic in CreateSharedNetworkForm and CreateL2NetworkForm. Reproduce the Add network flow and verify that the pre-selected offering is the first one with Required availability rather than simply the first offering in the ID-sorted list.

Written by the indexing model from the issue text.