[Identity] Avoid secret generation and slim down size of identity ser…

…ver docker image

Summary:
Secrets should not be generated as part of the docker image build. Instead, they need to be mounted in to the container.

Also reduces the image size from 1.81GB to 108MB.

https://linear.app/comm/issue/ENG-4419

Test Plan:
```
docker build -f services/identity/Dockerfile .
# or
cd services
docker compose build identity
```

Reviewers: varun, bartek

Reviewed By: varun, bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8580

.dockerignore

@@ -31,6 +31,7 @@ keyserver/*.env.*
 services/tunnelbroker/Dockerfile
 services/identity/target
 services/identity/Dockerfile
+services/identity/secrets
 services/backup/Dockerfile
 services/blob/target
 services/blob/Dockerfile

services/identity/Dockerfile

@@ -1,39 +1,37 @@
-FROM rust:1.67
+FROM rust:1.67 as builder
 
 RUN apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y \
   build-essential cmake git libgtest-dev libssl-dev zlib1g-dev \
-  && rm -rf /var/lib/apt/lists/*
+  && rm -rf /var/lib/apt/lists/* \
+  && mkdir -p /home/root/app/
+
+WORKDIR /home/root/app
 
 # Install more recent version of protobuf, must be ran as root
 COPY scripts/install_protobuf.sh ../../scripts/install_protobuf.sh
 RUN ../../scripts/install_protobuf.sh
 
-# Create a new user comm and use it to run subsequent commands
-RUN useradd -m comm
-USER comm
-
-# The build.rs script depends on rustfmt
-RUN rustup component add rustfmt
-
 RUN mkdir -p /home/comm/app/identity
 WORKDIR /home/comm/app/identity
-RUN cargo init --bin
 
-COPY services/identity/Cargo.toml services/identity/Cargo.lock ./
+COPY services/identity .
+COPY shared/protos/identity_client.proto ../../shared/protos/
 COPY shared/comm-opaque2 ../../shared/comm-opaque2
 
-# Cache build dependencies in a new layer
-RUN cargo build --release
-RUN rm src/*.rs
+RUN cargo install --locked --path .
 
-COPY services/identity .
-COPY shared/protos/identity_client.proto ../../shared/protos/
+FROM debian:bullseye-slim
+
+RUN apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y \
+  ca-certificates \
+  && rm -rf /var/lib/apt/lists/* \
+  && useradd -m comm
 
-# Remove the previously-built binary so that only the application itself is
-# rebuilt
-RUN rm ./target/release/deps/identity*
+WORKDIR /home/comm/app/identity
+
+COPY --from=builder /usr/local/cargo/bin/identity \
+  /usr/local/bin/identity
 
-RUN cargo build --release
-RUN target/release/identity keygen
+USER comm
 
-CMD ["./target/release/identity", "server"]
+CMD ["identity", "server"]