Support TLS Expiry alerts

[proffalken]

This is an amazing project, I had it up and running within minutes of your post on Reddit, thank you so much!

It would be awesome if you could add TLS monitoring alongside the "uptime" monitoring.

Although LetsEncrypt does a great job of auto-renewing certs, it would be great to monitor the following metrics as well:

1. Days until certificate expires
2. Whether the certificate is valid or invalid

I've been bitten by this so many times in the past!

[TheGuyDanish]

The ability to import a trusted root CA (for internal CA's) would be a welcome addition to the above.

[12nick12]

Adding to this domain expiration would also be great.

[joe-eklund]

The ability to import a trusted root CA (for internal CA's) would be a welcome addition to the above.

Hi I detailed how you can do this in #21 (comment) using an environment variable.

[tmarly]

Hi, I see that the commit #44c1b336 fix this issue and is in the latest version, am I wrong ?

[proffalken]

@tmarly nope, not wrong, this is working well in the latest version.

[jsloane]

Is there a way to disable these alerts? I don't want to be notified when the certificate is going to expire in 14 days, I just need outage notifications.

[chakflying]

See #844, config is currently not implemented yet.