[BUG] Cannot create AKS on subnet with routetable in Azure portal

[JoeyC-Dev]

Describe the bug
A clear and concise description of what the bug is.
Optional: Set the appropriate GitHub label(s) to indicate the AKS feature or area you believe your bug relates to.

Azure portal has an over-strict check to prevent user from creating AKS when subnet is bound with routetable.

To Reproduce
Steps to reproduce the behavior:

1. Create a subnet with routetable
2. Try to create AKS with BYO VNet, bound with that subnet
   

However, user does can create it via az-cli in the same subnet (no user-assigned managed identity required):

Expected behavior
A clear and concise description of what you expected to happen.

Should be able to create AKS via Azure portal when subnet is bound with routetable.

Environment (please complete the following information):

• CLI Version: 2.69.0
• Browser: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/133.0.0.0 Safari/537.36 Edg/133.0.0.0

[microsoft-github-policy-service]

Action required from @aritraghosh, @julia-yin, @AllenWen-at-Azure