Firebase function to handle CRUD

[NickHu]

I've made a start on implementing the Firebase function we'll need (acting as our backend) for create, read, update, delete operations. I had thought that this would need to be written in JavaScript, but as the Firebase functions runner uses the node runtime that means we can write it in Rust compiled to WASM 🎉. Not all that many HTTP server libraries actually manage to compile to WASM, so axum seems like the way to go.

To run the backend in the emulator, run either cargo make emulate-server or firebase emulators:start --only functions. If not using nix, you'll need to npm install first inside homotopy-server/js. The response can be obtained from http://localhost:5001/homotopy-io/europe-west2/api, as the emulator says.

[github-actions]

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_{(expires Wed, 14 Dec 2022 12:57:14 GMT)}

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