Transparent proxy ip range is not configurable

#### Feature Description

**No Configuration Parameters**: A review of Consul's service definition schema and configuration options shows no parameters for customizing the virtual IP range.

**Hardcoded Implementation in Source Code**: The virtual IP range is hardcoded in Consul's source code at:

**File**: `agent/consul/state/catalog.go` (lines 43-45)

```go
var (
// startingVirtualIP is the start of the virtual IP range we assign to services.
// The effective CIDR range is startingVirtualIP to (startingVirtualIP + virtualIPMaxOffset).
startingVirtualIP = net.IP{240, 0, 0, 0}

virtualIPMaxOffset = net.IP{15, 255, 255, 254}
)
```

This shows that:

- **Starting IP**: `240.0.0.0` (hardcoded as `net.IP{240, 0, 0, 0}`)
- **Maximum offset**: `15.255.255.254` (defining the upper bound)
- **Effective range**: `240.0.0.0` to `255.255.255.254` (the entire `240.0.0.0/4` block)

**File**: `agent/consul/state/catalog.go` (functions using these constants)

- `assignServiceVirtualIP()` - Assigns virtual IPs to services
- `addIPOffset()` - Performs IP arithmetic within the range
- `ServiceVirtualIP.IPWithOffset()` - Calculates final IP addresses

#### Use Case(s)

This ip range can be in use by other services which can cause possible ip duplication and network instabilities.