Add SSL cert renewals to the maintenance section

[orisdorch]

Guides > Network > Maintaining a Node -- should include reference to annual SSL certificate renewals. For bootstrap, renewCertificates makes this fairly simple.

Prospective references: https://github.com/fboucquez/symbol-bootstrap/blob/dev/docs/renewCertificates.md https://hackmd.io/@syndicate/rkhZiI09K https://discord.com/channels/856325968096133191/927674692557500506/1049797477802455191

Note: Including the recommendation to backup the /target folder (as indicated in bootstrap's docs) may be worth considering.