Update the docker build to include features based images (#3875)

## Proposed Changes

There are some features that are enabled/disabled with the `FEATURES` env variable. This PR would introduce a pattern to introduce docker images based on those features. This can be useful later on to have specific images for some experimental features in the future.

## Additional Info

We at Lodesart need to have `minimal` spec support for some cross-client network testing. To make it efficient on the CI, we tend to use minimal preset.

.github/workflows/docker.yml

@@ -43,7 +43,7 @@ jobs:
             VERSION: ${{ env.VERSION }}
             VERSION_SUFFIX: ${{ env.VERSION_SUFFIX }}
     build-docker-single-arch:
-        name: build-docker-${{ matrix.binary }}
+        name: build-docker-${{ matrix.binary }}${{ matrix.features.version_suffix }}
         runs-on: ubuntu-22.04
         strategy:
             matrix:
@@ -51,6 +51,10 @@ jobs:
                          aarch64-portable,
                          x86_64,
                          x86_64-portable]
+                features: [
+                    {version_suffix: "", env: ""},
+                    {version_suffix: "-dev", env: "spec-minimal"}
+                ]
                 include:
                     - profile: maxperf
 
@@ -60,6 +64,8 @@ jobs:
             DOCKER_CLI_EXPERIMENTAL: enabled
             VERSION: ${{ needs.extract-version.outputs.VERSION }}
             VERSION_SUFFIX: ${{ needs.extract-version.outputs.VERSION_SUFFIX }}
+            FEATURE_SUFFIX: ${{ matrix.features.version_suffix }}
+            FEATURES: ${{ matrix.features.env }}
         steps:
             - uses: actions/checkout@v3
             - name: Update Rust
@@ -98,7 +104,8 @@ jobs:
                   docker buildx build \
                       --platform=linux/${SHORT_ARCH} \
                       --file ./Dockerfile.cross . \
-                      --tag ${IMAGE_NAME}:${VERSION}-${SHORT_ARCH}${VERSION_SUFFIX}${MODERNITY_SUFFIX} \
+                      --tag ${IMAGE_NAME}:${VERSION}-${SHORT_ARCH}${VERSION_SUFFIX}${MODERNITY_SUFFIX}${FEATURE_SUFFIX} \
+                      --build-arg FEATURES=${FEATURES} \
                       --provenance=false \                      
                       --push
     build-docker-multiarch:

book/src/docker.md

@@ -57,7 +57,7 @@ $ docker pull sigp/lighthouse:latest-modern
 Image tags follow this format:
 
 ```
-${version}${arch}${stability}${modernity}
+${version}${arch}${stability}${modernity}${features}
 ```
 
 The `version` is:
@@ -81,6 +81,12 @@ The `modernity` is:
 * `-modern` for optimized builds
 * empty for a `portable` unoptimized build
 
+The `features` is:
+
+* `-dev` for a development build with `minimal-spec` preset enabled.
+* empty for a standard build with no custom feature enabled.
+
+
 Examples:
 
 * `latest-unstable-modern`: most recent `unstable` build for all modern CPUs (x86_64 or ARM)