Add last updated time for users/tenants/roles

[Joshua Harlow]

When a user/tenant/role gets updated it would be nice to have a 'last_updated' time of when that occurred. For those using a database to store this information it helps if said information exists so that 'stale' information can be cleaned (or users which no longer exist after X time can be dropped).

[Dolph Mathews (dolph)]

For consistency with other timestamps exposed by the API, this should be exposed as 'updated_at'; however, I'm not sure that all drivers could support this feature (e.g. identity.ldap?), so it may have to be an optional attribute at the API level.

[Eric Brown (ericwb)]

LDAP can have an attribute called "modifyTimestamp". I know OpenLDAP usually has it.

From RFC 4512:
   Entries may contain, among others, the following operational
   attributes:

      - creatorsName: the Distinguished Name of the user who added this
          entry to the directory,

      - createTimestamp: the time this entry was added to the directory,

      - modifiersName: the Distinguished Name of the user who last
          modified this entry, and

      - modifyTimestamp: the time this entry was last modified.