DOCSP-53342: Add converted .md docs to source code repo /docs dir for community access

Added new `docs/` dir to house the converted Kotlin SDK docs. - All pages are converted fully to Markdown - Any references to deprecated features or products were removed (e.g. App Services and Device Sync) - External links were preserved - Links to API references were removed since they pointed to `mongodb.docs` domain - Links to MongoDB, Atlas, or other Docs pages were removed