Realm deprecation

MongoDB has announced a [notice of deprecation](https://www.mongodb.com/docs/atlas/device-sdks/deprecation/#std-label-device-sdks-deprecation) for their Realm SDKs.

> As of September 2024, Atlas Device SDKs are deprecated. Atlas Device SDKs will reach end-of-life and be removed on September 30, 2025.

A bit more context about non-sync usage https://github.com/realm/realm-js/discussions/6884#discussioncomment-11111027:

> @liamjones good question. I'll try to clarify.
>
> are MongoDB ceasing internal development on the non-sync Realm SDKs
>
> To be clear, we're no longer doing active feature development on any of the SDKs: We're mostly in a "keep the lights on" mode for existing customers until everything goes EOL in less than a year from now. This goes for sync as well as non-sync parts of the product.
>
> how are PR merges to the community branch going to work?
>
> This is a good question and to be honest, as it involves speculation about the future, there's a limit to how accurately I'm able to answer it. To be honest, we haven't seen a large engagement from the community to provide PRs and in the current (low) rate I'd expect we'll (MongoDB engineers now assigned other teams within the company) be able to handle reviewing, merging and releasing for the foreseeable future.
>
> If however, someone from the community shows an interest in participating in the release and ongoing maintenance of the SDK, that would be welcomed and we'd be interested in talking through what that would look like in practice and any mutual expectations there might be.

(As well, a discussion in Realm dotnet's repo: https://github.com/realm/realm-dotnet/discussions/3676)

Since the Realm SDK we're using reaches EOL at the end of September this year, we should look into migrating to a different DB solution—unless a substantive community effort pledges to support development and maintenance going forward.

No files, tests, or entry points are named. Start by reviewing how the application currently uses the Realm SDK, then investigate replacement database options and the migration implications; done means an agreed migration plan or a documented decision to continue with community-supported Realm maintenance.

Written by the indexing model from the issue text.