Change default bind address to localhost for all exporters

### Description

For the security concern, we should bind all exporter to localhost only.
Ex: https://github.com/canonical/hardware-observer-operator/pull/463

- [ ] DCGMExporter
- [ ] HardwareExporter

### Charm revision

latest/stable

### Juju version

any

### Cloud

_No response_

### Expected behaviour

Default binding address should be localhost only

### Reproduce / Test

Install the hardware-observer charm and check the binding address and port of all exporters.

### Notes & References

_No response_

Install the hardware-observer charm and inspect how the DCGMExporter and HardwareExporter binding addresses are configured. Check each exporter’s listening address and port, then verify that every exporter defaults to localhost only, as described in the expected behaviour and the linked reference.

Written by the indexing model from the issue text.