the ways in which consul could be louder about a soon to expire certificate are potentially infinite

Consul v1.14.7

Repo steps:
1. Create a tls cert and wait around for it to get ready to expire
2. View the consul UI... or nomad UI
3. see nothing

```
Err: connection error: desc = "transport: Error while dialing tls: failed to verify certificate: x509: certificate has expired or is not yet valid
```

Seeing as now it's seemingly impossible to remedy this situation without taking all services offline, some warning would have been nice.

Ideas:
Maybe a big red/flashing message could show up in the consul UI when the TLS cert is nearing its expiration.

I suppose that applies to anything else that is an "ERROR" in the logs.

Start by reproducing the expired-certificate failure with Consul v1.14.7, then inspect the Consul UI and Nomad UI behavior described in the report. Define the warning scope and the expiration threshold before making changes; done should include a visible warning before expiry and a way to verify it during the TLS failure scenario.

Written by the indexing model from the issue text.