## Description 

This PR adds the `user-agent` header for the faucet requests to keep
track which requests come from where.
The CLI gets updated to make usage of this header when requesting a
token via `sui client faucet`.

## Test plan 

Locally, fired up a grafana dashboard and also looked at the prometheus
metrics.
`total_requests_received{path="/v1/gas",user_agent="sui/1.39.0"} 1`

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## Release notes

Check each box that your changes affect. If none of the boxes relate to
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that describes the impact of your changes that a user might notice and
any actions they must take to implement updates.

- [ ] Protocol: 
- [ ] Nodes (Validators and Full nodes): 
- [ ] Indexer: 
- [ ] JSON-RPC: 
- [ ] GraphQL: 
- [ ] CLI: 
- [ ] Rust SDK:
- [ ] REST API: