support reloading service configuration on SIGHUP

[kevinschoonover]

Is your feature request related to a problem? Please describe.
If the consul token is ever rotated in a service configuration on disk, vault will never pick up the changes and will be unable to perform future service registrations. Added more specific details in #17598

Describe the solution you'd like
I created the following PR to solve the problem #17598

Additional context
I rotate the consul token roughly every 7 days and deployed this code in a forked version of vault in my infrastructure and haven't had any issues.