feat: support to execute pre-build commands

As we known, some libraries are required to be installed when we
use some gems, this feature make it possible.

action.yml

@@ -32,6 +32,9 @@ inputs:
   jekyll_baseurl:
     description: 'The Jekyll website baseurl'
     required: false
+  pre_build_commands:
+    description: 'The pre-build commands'
+    required: false
 runs:
   using: 'docker'
   image: 'Dockerfile'

entrypoint.sh

@@ -15,6 +15,7 @@ BUNDLER_VER=${INPUT_BUNDLER_VER:=>=0}
 JEKYLL_SRC=${INPUT_JEKYLL_SRC:=./}
 JEKYLL_CFG=${INPUT_JEKYLL_CFG:=./_config.yml}
 JEKYLL_BASEURL=${INPUT_JEKYLL_BASEURL:=}
+PRE_BUILD_COMMANDS=${INPUT_PRE_BUILD_COMMANDS:=}
 
 # Set default bundle path and cache
 BUNDLE_PATH=${WORKING_DIR}/vendor/bundle
@@ -41,6 +42,12 @@ fi
 
 cd ${JEKYLL_SRC}
 
+# Check and execute pre_build_commands commands
+if [[ ${PRE_BUILD_COMMANDS} ]]; then
+  echo "Executing pre-build commands"
+  eval "${PRE_BUILD_COMMANDS}"
+fi
+
 echo "Initial comptible bundler"
 ${SCRIPT_DIR}/script/cleanup_bundler.sh
 gem install bundler -v "${BUNDLER_VER}"