util.startup: Support systemd Type=notify service type
This lets Prosody report its lifecycle status to systemd, so it knows
when Prosody has completed its startup, when it's reloading and shutting
down.
Both Type=notify and Type=notify-reload is supported
Example systemd .service configuration snippet:
[Service]
Type=notify
.DEFAULT: localhost.crt
keysize=2048
# How to:
# First, `make yourhost.cnf` which creates a openssl config file.
# Then edit this file and fill in the details you want it to have,
# and add or change hosts and components it should cover.
# Then `make yourhost.key` to create your private key, you can
# include keysize=number to change the size of the key.
# Then you can either `make yourhost.csr` to generate a certificate
# signing request that you can submit to a CA, or `make yourhost.crt`
# to generate a self signed certificate.
${.TARGETS:M*.crt}:
openssl req -new -x509 -newkey rsa:$(keysize) -nodes -keyout ${.TARGET:R}.key \
-days 365 -sha256 -out $@ -utf8 -subj /CN=${.TARGET:R}
.SUFFIXES: .key .crt