feat (cht-android/issues/310) enable nginx to serve android app links

[mrjones-plip]

Description

Initial PR to enable nginx container to serve static JSON files for android asset links:

See cht-android/issues/308

Code review checklist

• Readable: Concise, well named, follows the style guide, documented if necessary.
• Documented: Configuration and user documentation on cht-docs
• Tested: Unit and/or e2e where appropriate
• Internationalised: All user facing text
• Backwards compatible: Works with existing data and configuration or includes a migration. Any breaking changes documented in the release notes.

Compose URLs

If Build CI hasn't passed, these may 404:

• Core
• CouchDB Single
• CouchDB Cluster

License

The software is provided under AGPL-3.0. Contributions to this project are accepted under the same license.

[mrjones-plip]

After chatting with @kennsippell - I think we should take a different approach for this. Instead of allowing nginx to directly serve up a static JSON file as done here, we should update CHT Conf to have an settings, mainly the app ID and cert hash, and then server this up at the right location (/.well-known/assetlinks.json). This latter approach allows all the CHT config to logically be stored in one place (app settings) and not have to worry about static files outside of the CHT purview.

Leaving this PR open and as is in case anyone wants to test.

[garethbowen]

@mrjones-plip Can we close this PR now? Happy to keep the branch around for testing purposes just trying to clean up old PRs!

[mrjones-plip]

agreed - thanks for the house cleaning Gareth! 🏠 🧽