[cisco_meraki_metrics] Add support for vpn metrics

Add support for the below vpn monitoring metrics for cisco meraki metrics integration.

`GET /networks/{networkId}/appliance/vpn/statuses
`

`GET /organizations/{organizationId}/appliance/vpn/stats
`

These stats include:

### Reachability:

- wan1.reachability
- wan2.reachability
- Data Usage (in Kilobytes):
- wan1.receivedInKilobytes
- wan2.receivedInKilobytes
- wan1.sentInKilobytes
- wan2.sentInKilobytes

### Jitter (in milliseconds):

- wan1.avgJitter
- wan1.maxJitter
- wan1.minJitter
- wan2.avgJitter
- wan2.maxJitter
- wan2.minJitter

### Latency (in milliseconds):

- wan1.avgLatencyMs
- wan1.maxLatencyMs
- wan1.minLatencyMs
- wan2.avgLatencyMs
- wan2.maxLatencyMs
- wan2.minLatencyMs

### Packet Loss (in percentage):

- wan1.avgLossPercentage
- wan1.maxLossPercentage
- wan1.minLossPercentage
- wan2.avgLossPercentage
- wan2.maxLossPercentage
- wan2.minLossPercentage

Mean Opinion Score (MOS):

- wan1.avgMos
- wan1.maxMos
- wan1.minMos
- wan2.avgMos
- wan2.maxMos
- wan2.minMos