Export app-crypto specific keystore functions (#7489)

* Export app-crypto specific keystore functions

* Also add back the insert function

* Switch KeystoreContainer to an enum

* Only export the bare minimal for LocalKeystore and fix service compile

* fix: should return Arc

* Add docs stating that functions only available in local keystore

* Remove insert and generate functions

* fix: generate function should be available in test

* Add keypair function to trait

* Revert "Add keypair function to trait"

This reverts commit ad921b09.

* Add note for local_keystore function in service