caddyfile: Allow overriding server names

[francislavoie]

Fix #5322

[emilylange]

Breaks when two different servers are called the same:

{
	servers :443 {
		name https
	}

	servers :8000 {
		name https
	}
}

example.com {
}

:8000 {
}

{
    "apps": {
        "http": {
            "servers": {
                "https": {
                    "listen": [
                        ":8000"
                    ]
                }
            }
        }
    }
}

[francislavoie]

Ah right, I should reject duplicate names.

[mholt]

Thanks. This is something I hoped we wouldn't really have to care about... but here we are. 😅