GHA: use a JavaScript action

The composite action didn't work as expected (the action's
`action.sh` and `build.sh` weren't accessible), so I replaced the
shell script with a tiny JavaScript bootstrap, that will properly
collect the action inputs and generate a simple local build.sh and
calls it.

Note that we couldn't use a Docker container action, because we
couldn't access the host docker ending, and would need to add both
docker cli and docker server to the docker container...

action.js

@@ -0,0 +1,35 @@
+const process = require("process")
+const { spawn } = require("child_process")
+const fs = require("fs")
+
+// basic implementation of @action/core.getInput()
+function getInput(name) {
+  return process.env[`INPUT_${name.toUpperCase()}`].trim()
+}
+
+// collect action inputs:
+let setupOpts = []
+if (getInput("skip-login") === "true") setupOpts.push("--skip-login")
+if (getInput("latest") === "true")     setupOpts.push("latest")
+
+let buildOpts = [], value
+if ((value = getInput("repository")) !== "")        buildOpts.push(`-r ${value}`)
+if ((value = getInput("repository-suffix")) !== "") buildOpts.push(`-s ${value}`)
+if ((value = getInput("tag-suffix")) !== "")        buildOpts.push(`-t ${value}`)
+if ((value = getInput("build-directory")) !== "")   buildOpts.push(`-d ${value}`)
+if ((value = getInput("build-options")) !== "")     buildOpts.push(`-o "${value}"`)
+
+// generate a local build.sh script:
+fs.writeFileSync("build.sh", `#! bash
+source ${__dirname}/build.sh
+dockerSetup ${setupOpts.join(" ")}
+echo $VERSION > VERSION
+dockerBuildAndPush ${buildOpts.join(" ")}
+`)
+
+// execute it:
+const build = spawn("bash", ["build.sh"], { maxBuffer: 100 * 1024 * 1024 })
+build.stdout.on("data", data => { process.stdout.write(data) })
+build.stderr.on("data", data => { process.stderr.write(data) })
+build.on("error", error => { console.error(error) })
+build.on("exit", code => { process.exit(code) })

action.yml

@@ -26,16 +26,5 @@ inputs:
     type: string
 
 runs:
-  using: composite
-
-  steps:
-    - run: ./action.sh
-      env:
-        INPUT_SKIP_LOGIN: ${{ inputs.skip-login }}
-        INPUT_LATEST: ${{ inputs.latest }}
-        INPUT_REPOSITORY: ${{ inputs.repository }}
-        INPUT_REPOSITORY_SUFFIX: ${{ inputs.repository-suffix }}
-        INPUT_TAG_SUFFIX: ${{ inputs.tag-suffix }}
-        INPUT_BUILD_DIRECTORY: ${{ inputs.build-directory }}
-        INPUT_BUILD_OPTIONS: ${{ inputs.build-options }}
-      shell: bash
+  using: node16
+  main: action.js