Do not require HTTPS on Tailscale VPN subnet 100.64.0.0/10

**Describe the bug**
When trying to add my own RPC node that I connect to via Wireguard (using Tailscale) on HTTP, MetaMask mobile refuses to do so and wrongly requires HTTPS.

**Screenshots**

**To Reproduce**
1. Add a network
2. Set your own RPC node URL

**Expected behavior**
Being able to add the network.
MetaMask should not require HTTPS in the `100.64.0.0/10` subnet as it’s a private Tailscale VPN the same way it doesn’t require HTTPS on `192.168.0.0/16`.
More details on https://tailscale.com/kb/1015/100.x-addresses/

**Smartphone (please complete the following information):**
- Device: Pixel 6 Pro
- OS: Android 12
- App Version: 5.5.0 (939)

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_to be added after bug submission by internal support / PM_
**Severity**

- How critical is the impact of this bug on a user?
- Add stats if available on % of customers impacted
- Is this visible to all users?
- Is this tech debt?

Start with the add-network flow and trace the RPC URL HTTPS validation, comparing its existing 192.168.0.0/16 exception with 100.64.0.0/10. Done means a Tailscale subnet HTTP URL can be added while HTTPS remains required elsewhere; verify the reproduction on Android.

Written by the indexing model from the issue text.