[RFE] prometheus endpoint is bound to `db`

[Peter Jose De Sousa]

Hello,

When configuring the ETCD charm there is an prometheus endpoint to bind to, this endpoint is typically where we would host the prometheus DB.

Typically we would want etcd to expose prometheus on a internal network, which is not private (e.g. provider, or public company subnet). Whereas `db` would be on an internal network, as it's the database/coordination for Vault.

This bug is to request that the `db` endpoint for prometheus targets be changed to `prometheus` to enable the separation of configuration between vault:db/prometheus:target networking.

Thanks,
Peter