NGINX: Reload NGINX on certificate renewal

[lmagyar]

fixes #2870 #2725 #2600

This modification checks daily (crond default daily 02:00:00) whether the configured certificate file has been changed and reloads (not restarts) nginx to pick up the new certificate.

• If there is no backup connection to the device (eg. ssh, cloud, vpn), we can lose access to it. In case of a remote, not regularly updated device, this can be a real problem.
• DuckDNS add-on checks the certificate in each 12h.
• Letsencrypt renews the certificate if it expires within the next 30 days and did not revoke the previous certificate.
• So checking certificate renewal daily should be fine.

It also uses the new s6-overlay layout.

s6-rc: info: service nginx: starting
s6-rc: info: service s6rc-oneshot-runner: starting
s6-rc: info: service nginx successfully started
s6-rc: info: service crond: starting
s6-rc: info: service s6rc-oneshot-runner successfully started
s6-rc: info: service fix-attrs: starting
s6-rc: info: service crond successfully started
s6-rc: info: service fix-attrs successfully started
s6-rc: info: service legacy-cont-init: starting
s6-rc: info: service legacy-cont-init successfully started
s6-rc: info: service legacy-services: starting
s6-rc: info: service legacy-services successfully started
[21:09:33] INFO: Running nginx...
[02:00:00] INFO: Reloading nginx to reload new certificate file

[lmagyar]

FYI: Real life test result.

One of my certificates got renewed on Apr. 12 by DuckDNS:

 131126 -rw-------    1 root          5406 Apr 12 19:24 fullchain.pem
 131127 -rw-------    1 root           359 Apr 12 19:24 privkey.pem

The original add-on, didn't reload it:

[06:34:29] INFO: Running nginx...

And serves the old certificate (this is the cert info from FF):

Not Before: Sat, 11 Feb 2023 15:12:53 GMT
Not After:  Fri, 12 May 2023 15:12:52 GMT

---

Meanvile the add-on modified by this PR, reloaded the new cert:

[06:34:34] INFO: Running nginx...
[02:00:00] INFO: Reloading nginx to reload new certificate file

And we get it in the browser (this is the cert info from FF):

Not Before: Wed, 12 Apr 2023 16:24:44 GMT
Not After:  Tue, 11 Jul 2023 16:24:43 GMT

After 12 May 2023 15:12:52 GMT I can test whether I loose the connection to the official add-on or the modified.