Implement WebDav document store provider

[yurem]

We need to implement interface: https://github.com/GluuFederation/oxCore/blob/version_4.1.1/core-document-store/src/main/java/org/gluu/service/document/store/provider/WebDavDocumentStoreProvider.java

We can use:

<dependency>
    <groupId>com.github.lookfirst</groupId>
    <artifactId>sardine</artifactId>
    <version>5.9</version>
</dependency>

This library is fully stable and is being used in production on a very high traffic site (140+ concurrent connections 24/7).