Limited use trusts

Trusts now have a "remaining_uses" field that tracks how many times
a trust can still issue a token. It is decremented by 1 each time a
trust related authentication occurs (call to /auth/tokens), until it
reaches 0 and no token can be issued through this trust anymore. If
set to null (default value), trusts can be used indefinitely to
authenticate.

Closes-Bug: #1250617
Implements: bp trusts-chained-delegation
DocImpact
Co-Authored-By: Florent Flament <florent.flament-ext@cloudwatt.com>

Change-Id: I2c80b6d548a6715da0366c6f64ee58fbce514adb
Merge "Limited use trusts"