maintain a static map of trusted roles for resource list lookup api

[havetisyan]

Description

when we get large number of simultaneous listResourceAccess calls, all try to get the current list of trust roles setup in the server. This could get quite large so all the threads are busy getting large number of rows from DB. However, in most cases, those never change so there is no need to fetch the list for every request. So now we're maintaining a static map of the roles to address the case with large simultaneous calls:
a) by default we drop the map every 10 minutes so any deletions to the rows can be reflected in 10 minutes. This could be changed by the specifying the different value for the athenz.zms.mysql_server_trust_roles_update_timeout property value in milliseconds (default 600,000).
b) we check the last modification timestamp of the policy that has an assertion with assume_role action. this way new assertions are in effect immediately

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• The pull request does not introduce any breaking changes
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