[Uptime] Add validation for < 1 values in TLS expiration fields

[andrewvc]

It is currently possible to use negative values for TLS expiration in uptime. This makes no sense. We should use the form validator code to mark the form as in an error state if the values are < 1 or are non-integers.

[elasticmachine]

Pinging @elastic/uptime (Team:uptime)