Generated hostnames never report that their DNS record is programmed

[0xmc]

What needs to happen

Every hostname on a proxy should report the same set of conditions, whether the user brought the name or we generated it. A hostname we generate reports only that it was claimed and that it is covered by a certificate; the condition saying its DNS record has been programmed never appears, even after the name resolves. A user who wrote a wait loop around that condition, straight from our documentation, polled for four minutes against a hostname that had already been resolving for three of them.

Why this matters

This is the documented way to know a proxy is usable, and for the hostname most people get first it never becomes true. Anyone automating a deploy has to discover by experiment that the condition they were told to wait for only exists on custom hostnames, then write two code paths. A closely related timing problem on custom hostnames is tracked in custom hostname programming latency; this one is about the condition being absent altogether.

The same report flagged a second, smaller version of the same issue: the schema says the system may automatically generate a hostname. It always does. Stating that plainly removes a branch an agent otherwise has to test for.

Desired outcome

• A generated hostname reports whether its DNS record is programmed, on the same condition the documentation tells people to wait for
• One wait loop works for both generated and user-supplied hostnames
• If the condition is deliberately not applicable to generated hostnames, the documentation says which condition to wait for instead
• The hostname field's description states that a hostname is always generated, rather than that one may be

Related to #291