Change default SecretLeaseContainer.leaseEndpoints from Legacy to Leases

[ThomasKasene]

As suggested in #588, maybe the time is ripe for replacing the default selection of SecretLeaseContainer.leaseEndpoints from LeaseEndpoints.Legacy to LeaseEndpoints.SysLeases, or alternatively, the new option that's being added in #588?

[ThomasKasene]

Correction: #588 now deprecates LeaseEndpoints.SysLeases, so the new default should be one of these instead:

• LeaseEndpoints.Leases
• LeaseEndpoints.LeasesRevokedByPrefix

[mp911de]

That's in place now.