enable hierarchical path for library sets

[fairclothjm]

Phase 3 of https://github.com/hashicorp/vault-plugin-secrets-openldap/pull/102 and https://github.com/hashicorp/vault-plugin-secrets-openldap/pull/104

This PR adds hierarchical path handling to the following APIs:

• Library set management
• Library set status check
• Check-Out management
• Check-In management