Docs: Feedback for Implementing a Custom MapStore

Hi, I have some feedback about [this page](https://github.com/hazelcast/hz-docs/edit/main/docs/modules/mapstore/pages/implement-a-mapstore.adoc)

on this page the full example on YourMapStoreImplementation is loss, please fix it.
and there is another feedback also about how to write a MapStoreImplementation, in this page, there is a MongoDB client example, and add two fields named MongoClient mongoClient; MongoCollection collection; if I use other database which not support in Types of Data Connections, like SurrealDB. how to write it, it's better to give another more examples and details . thanks for read this.

Start with docs/modules/mapstore/pages/implement-a-mapstore.adoc and inspect the YourMapStoreImplementation example and the MongoDB client example. Restore the missing full example, clarify the MongoDB fields, and add guidance or examples for custom databases such as SurrealDB. Done means the page covers both supported and unsupported database connections clearly.

Written by the indexing model from the issue text.