The graceful manager waits for 4 listeners to be created or to be told that they are not needed. If it is not told about them it will indefinitely and timeout.
This leads to SVC hosts not being told of being in the readyState but on Unix would lead to the termination of the process.
There was an unfortunate regression in #20299 which missed this subtly and in the case whereby SSH is disabled the `builtinUnused()` is not called.
This PR adds a call to `builtinUnused()` when not using the builtin ssh to allow `createServerWaitGroup.Done()` to be called.
In addition it was noted that the if/else clauses for timeout informing of the SVC host were in the wrong order. These have been swapped.
Fix#20609
Backport #20299. Follow #20298. Only the `GlobalInitInstalled` function should prepare the SSH files for external server or starts the builtin server.
* `trustedUserCaKeys` is removed, use `SSH.TrustedUserCAKeys` directly
* introduce `ssh.Init`, move the SSH init code from `routers/init.go` to it
* `ssh.Init` will start builtin SSH server or prepare external SSH server files
