Adds docs note about using wildcard address for PG when setting up Geo

What does this MR do?

If using 0.0.0.0 or * in the PostgreSQL listen_address, Rails and PG client libraries will attempt to use 127.0.0.1, this adds a note to include that in the md5_auth_cidr_addresses if that is the case.

Related issues

Closes omnibus-gitlab#5258 (closed)

Also related - omnibus-gitlab!4133 (closed) was a suggestion to add this as a default to trust_auth_cidr_addresses.

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