Expand remote keystore interface to allow for hybrid mode (#7628)

* update to latest master

* updates on docs, license, meta

* hide ssrs behind feature flag

* implement remaining functions on the server

* sign server line length fix

* fix tests

* fixup in-memory-keystore

* adding failsafe

* skipping ecdsa test for now

* remote keystore param

* remote sign urls made available

* integrating keystore remotes features

* don't forget the dependency

* remove old cruft

* reset local keystore

* applying suggestions

* Switch to single remote, minor grumbles

* minor grumbles, docs