Feature Request: Reconnect on a timer

[ConnorRigby]

GCP requires using JTWs instead of TLS. Part of the JWT is an exp field that specifies the time in which the JWT expires. GCP boots the connection at that time. Since tortoise311 has it's config supplied via supervision specs, it just tries to use the same JWT over and over
again.

I think there are two parts to building this:

1. allow reconfiguring a connection with a new set of credentials
2. create an optional timer that specifies when the credentials expire

I'm happy to implement said feature, just want to get a discussion on it before starting.

Thanks so much!