support a list of IPs in the bind_ip configuration option

[Robert Gildein]

Right now `bind_ip` configuration option supports only
0.0.0.0 or 127.0.0.0 IP. Since MongoDB 3.6 supports the
list of IPs [1], I think that `bind_ip' should also support
the list of values.

Right now, if a private IP is configured, the charm will
fail because multiple functions are using "localhost" to
connect to MongoDB and "localhost" is blocked.

I think that solution will be to support list of IPs and
"localhost" (127.0.0.1) should be always append to the list.
Perhaps a private IP (for each unit) could also be added to
the list by default.

[1]: https://www.mongodb.com/docs/v3.6/administration/configuration/#security-considerations

[Eric Chen (eric-chen)]

This charm is no longer being actively maintained. Please consider using the new mongodb-k8s-operator instead.
https://github.com/canonical/mongodb-k8s-operator
I will close this feature request