[BugBash][Portal] Free instance should not enable create private endpoint in network tab

[vwxyzh]

Describe the bug

Free instance should not enable create private endpoint in network tab.

To Reproduce

1. Open portal.
2. Create a free instance.
3. Go to Networking tab.
4. Click Private access, then + Private endpoint, then enter some names, next, next, create.
5. The operation will be failed, since Free trier do not support private endpoint.

We should disable the button instead of create it, then fail.