Test nginx configuration before reload

[stefansundin]

Test the nginx configuration before reloading. This avoids crashing the container if there are configuration errors.

This makes the behavior similar to the nginx systemctl service which tests the nginx configuration before reload to avoid the same issue.

ExecStartPre=/usr/sbin/nginx -t

Fixes #206.

Log output on valid configuration:

examples-nginx-certbot-1  | 2023/09/22 21:28:36 [info] Received SIGHUP signal; terminating the autorenewal sleep process
examples-nginx-certbot-1  | Terminated
examples-nginx-certbot-1  | 2023/09/22 21:28:36 [info] Running the autorenewal service
examples-nginx-certbot-1  | 2023/09/22 21:28:36 [info] Starting certificate renewal process
examples-nginx-certbot-1  | nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
examples-nginx-certbot-1  | nginx: configuration file /etc/nginx/nginx.conf test is successful
examples-nginx-certbot-1  | 2023/09/22 21:28:36 [notice] 407#407: signal process started
examples-nginx-certbot-1  | 2023/09/22 21:28:36 [notice] 68#68: signal 1 (SIGHUP) received from 407, reconfiguring
examples-nginx-certbot-1  | 2023/09/22 21:28:36 [notice] 68#68: reconfiguring
examples-nginx-certbot-1  | 2023/09/22 21:28:36 [info] Autorenewal service will now sleep 8d

Log output on invalid configuration:

examples-nginx-certbot-1  | 2023/09/22 21:29:09 [info] Received SIGHUP signal; terminating the autorenewal sleep process
examples-nginx-certbot-1  | Terminated
examples-nginx-certbot-1  | 2023/09/22 21:29:09 [info] Running the autorenewal service
examples-nginx-certbot-1  | 2023/09/22 21:29:09 [info] Starting certificate renewal process
examples-nginx-certbot-1  | 2023/09/22 21:29:09 [emerg] 321#321: unexpected end of file, expecting ";" or "}" in /etc/nginx/conf.d/example_server.conf:10
examples-nginx-certbot-1  | nginx: [emerg] unexpected end of file, expecting ";" or "}" in /etc/nginx/conf.d/example_server.conf:10
examples-nginx-certbot-1  | nginx: configuration file /etc/nginx/nginx.conf test failed
examples-nginx-certbot-1  | 
examples-nginx-certbot-1  | 
examples-nginx-certbot-1  | 2023/09/22 21:29:09 [error] Nginx configuration is invalid, skipped reloading. Check the logs for details.
examples-nginx-certbot-1  | 
examples-nginx-certbot-1  | 2023/09/22 21:29:09 [info] Autorenewal service will now sleep 8d

[JonasAlfredsson]

Sorry for the delay, a real bad cold had me offline for almost a week.
I think you have made enough valid points to have this merged, however, I will still make this a major release since I do believe it alters the behavior enough that users should be aware of it.