Set custom process title in worker processes

When i use the `--tag` option, the master processes look like

```
puma 2.10.2 (tcp://0.0.0.0:44331) [vendors]
puma 2.10.2 (tcp://0.0.0.0:44335) [admin]
```

but the worker processes look like 

```
puma: cluster worker 0: 17854
puma: cluster worker 0: 17840
```

It would be very handy if the puma worker processes contained the tag in the process title as well.
