dist(docker): add curl package to Labrinth image, some other minor tweaks (#3915)

* dist(docker): add `.dockerignore` as symlink to `.gitignore`

This ensures that no files outside of version control are transferred to
the Docker build context for Labrinth and Daedalus images, which
significantly improves build speed (if a `target` directory is already
present) and build reproducibility.

* chore(dist/docker): simplify out unneeeded statements, move `SQLX_OFFLINE` env var setting to build command itself

The latter approach ensures that developers building the image locally
don't forget to set `SQLX_OFFLINE`, too.

* dist(docker): add `curl` package to Labrinth image

apps/daedalus_client/Dockerfile

@@ -1,5 +1,4 @@
 FROM rust:1.88.0 AS build
-ENV PKG_CONFIG_ALLOW_CROSS=1
 
 WORKDIR /usr/src/daedalus
 COPY . .
@@ -10,11 +9,8 @@ FROM debian:bookworm-slim
 
 RUN apt-get update \
   && apt-get install -y --no-install-recommends ca-certificates openssl \
-  && apt-get clean \
   && rm -rf /var/lib/apt/lists/*
 
-RUN update-ca-certificates
-
 COPY --from=build /usr/src/daedalus/target/release/daedalus_client /daedalus/daedalus_client
 WORKDIR /daedalus_client