Public cloud databases new mongodb guides v2

[thild42]

mongodb_17_why_mongodb

The guide is OK as is.

https://github.com/ovh/docs/tree/7e470a40acf6b89702efbb262a946765965e9656/pages/public_cloud/public_cloud_databases/mongodb_18_cluster_sizing

I made some minor fixes. Some chapters of this document are either redundant with other guides or should be ported as dedicated guides. "Connecting to MongoDB Database with MongoDB Compass" should link to mongodb_07_connect_compass. "Insert and Query Data" should be a dedicated short guide. "MongoDB Developer Best Practices" should be a dedicated short guide.

mongodb_19_migrate_to_ovhcloud

I made some minor fixes. I have removed the "blank.txt" file. The guide is now OK.

mongodb_20_relational_migrator

I made some minor fixes. The guide is now OK.

mongodb_21_operational_best_practices

I made some minor fixes. I have updated the links to use relative paths. One link needs to be changed as a result of the changes made in mongodb_18_cluster_sizing

mongodb_22_benchmark

I made some minor fixes. Links need to be updated with best practice guide.

mongodb_23_kafka_connector

I made some minor fixes. Images need to be scaled down

mongodb_24_read_preference_and_write_concern

I made some minor fixes. The guide is now OK.

mongodb_25_bi_connector

I made some minor fixes. The guide is now OK.

mongodb_26_k8s_operator

I made some minor fixes. The guide need to either be migrated to K8S section or simply removed.