Consider adding auto-refresh client feature

[dlongley]

It may make sense for instance configs to have a zcap that can be used to hit a refresh service that will auto-generate all zcaps stored in the config (including the refresh zcap itself). If so, there should be a core feature that automatically performs this functionality, similar to the metering reporting system that automatically runs.

[dlongley]

This generalized feature should include the zcap reference ID(s) or invocation targets that the auto-refresh zcap(s) are for so they can be mapped properly to the zcaps that need refreshing.

See also: digitalbazaar/bedrock-profile-http#55 (comment)