Previously, this used the PostgresFirewallRule related to the
PostgresResource. With the switch to using customer firewalls
and customer subnets for PostgresResources, PostgresFirewallRule
is an unnecessary abstraction.

Add port to API responses for postgres firewall rules. This previously
wasn't needed because each postgres firewall rule was for 2 ports, but
now that each port is handled by a separate rule, the port is needed to
disambiguate.  Temporarily, use 5432 if it is a PostgresFirewallRule,
but that will be going away shortly.

If the customer firewall allows other ports, they will not be
shown in this view. This is designed for keeping as much
backwards compatibility as possible while removing
PostgresFirewallRule. For full information on firewall rules,
the private subnet for the Postgres database should be used.
Add PostgresResource#pg_firewall_rules to handle this filtering.

To avoid duplicate queries, have postgres_require_customer_firewall!
helper return the firewall if it is found.

Temporarily, have the openapi.yml configuration allow either
pf or fr ubids for PostgresFirewallRule. This will eventually be
switching to all fr when the conversion is complete.

This makes it similar to the GET firewall-rule route. This has
a larger effect, the SDK/CLI use this.

For the CLI, include the port and description when showing the rule.

Instead of inserting 1 PostgresFirewallRule. This is a little
awkward, since we can return only one rule. Return the 5432 rule
in this case.

Use the same description for both created FirewallRules.

… ubids

Add PostgresResource#pg_firewall_rule{,s_dataset} to make it easier
to retrieve a specific rule.

Make PrivateSubnet#update_private_subnet_firewall_rules public,
so it can be called in the routes.

Update openapi.yml to remove use of pf ubids. The
postgres_firewall_rule_id component can be switched to firewall_rule_id.

This removes the last usage of PostgresFirewallRule in the routes.
The serializer still refers to PostgresFirewallRule, but it operates
on FirewallRule instances only now.

No longer create PostgresFirewallRule instances when creating
PostgresResources. Create FirewallRule instances instead.

Remove PostgresResource firewall_rules association and
set_firewall_rules method. Add a before_destroy so the
postgres_firewall_rule entries will be removed before the
resource is destroyed.

This does not drop the table. That can be done in later,
and requires multiple steps (delete all records, drop
before_destroy, drop postgres_firewall_rule table).

This keeps the update_firewall_rules semaphore for
PostgresResource, but makes it a no-op. That can also
be cleaned up later.

Update regen-screenshots to handle networking changes. It's showing:

Missing screenshots:
managed-postgresql/metrics-1-screenshot.png
managed-postgresql/metrics-2-screenshot.png

But I think that is unrelated to this change.