collab: Override Cargo configuration in the Dockerfile (#17901)

This PR moves the override for the Cargo configuration for collab into
the `Dockerfile` rather than having it be something some in the external
environment.

This makes it possible to build the Docker image locally without having
to replace `.cargo/config.toml` with the contents of
`.cargo/collab-config.toml`.

Release Notes:

- N/A

Dockerfile

@@ -4,6 +4,9 @@ FROM rust:1.81-bookworm as builder
 WORKDIR app
 COPY . .
 
+# Replace the Cargo configuration with the one used by collab.
+COPY ./.cargo/collab-config.toml ./.cargo/config.toml
+
 # Compile collab server
 ARG CARGO_PROFILE_RELEASE_PANIC=abort
 ARG GITHUB_SHA