[FEATURE REQUEST] Add vault_lease beacon module

[lkubb]

Is your feature request related to a problem? Please describe.
Secret backends other than the KV one usually issue leases that expire with time. If one wants to leverage Salt to manage these leases, there should be a process that:

1. periodically renews the leases (this is achieved by just requesting them from the store regularly)
2. warns when they cannot be extended anymore or have expired

Describe the solution you'd like
Add a beacon module that monitors a lease and warns when it runs out.

Describe alternatives you've considered
This could also be achieved with an engine module, especially 1.. 2. is the definition of the use case for a beacon module. Since there is also functionality in Salt to create a beacon when running a state (mod_beacon), it would make sense to use a beacon for 2..

The already implemented expiry events only work when a Salt invocation requests the lease.