Add support for Hashicorp LDAP secrets engine

[soklakov]

According to https://docs.spring.io/spring-cloud-vault/reference/secret-backends.html and https://docs.spring.io/spring-vault/reference/vault/vault-secret-engines.html currently there is no built-in support for Hashicorp LDAP secrets engine (https://developer.hashicorp.com/vault/docs/secrets/ldap).

I'd like you to add it because Hashicorp LDAP secrets engine supports a password rotation and it would be nice to have such integration out of the box.

[mp911de]

Sounds a good enhancement. For databases, we've built some abstractions to centralize common structures. For LDAP, it would make sense to build something on its own that isn't related to databases. Setting up a test environment for LDAP would be likely a lot of overhead, so we could start with an initial set of operations for dynamic credentials.

Feel free to submit a pull request.