[#368] design: StrategyMatrix API

I can't run the project for now because of a timeout

library/src/main/kotlin/it/krzeminski/githubactions/dsl/expressions/contexts/MatrixContext.kt

@@ -0,0 +1,21 @@
+package it.krzeminski.githubactions.dsl.expressions.contexts
+
+import it.krzeminski.githubactions.dsl.expressions.expr
+import kotlin.reflect.KProperty
+
+
+public open class StrategyMatrix(
+    private val map: MutableMap<String, List<String>> = mutableMapOf()
+): Map<String, List<String>> by map {
+
+    public fun iterate(vararg value: String): Property {
+        return Property(value.toList())
+    }
+
+    public inner class Property(public val values: List<String>) {
+        public operator fun getValue(strategyMatrixContext: StrategyMatrix, property: KProperty<*>): String {
+            map[property.name] = values
+            return expr("matrix.${property.name}")
+        }
+    }
+}

library/src/test/kotlin/it/krzeminski/githubactions/dsl/expressions/MatrixExample.kt

@@ -0,0 +1,51 @@
+package it.krzeminski.githubactions.dsl.expressions
+
+import it.krzeminski.githubactions.actions.actions.SetupNodeV3
+import it.krzeminski.githubactions.domain.RunnerType
+import it.krzeminski.githubactions.domain.triggers.Push
+import it.krzeminski.githubactions.dsl.expressions.contexts.StrategyMatrix
+import it.krzeminski.githubactions.dsl.workflow
+import it.krzeminski.githubactions.yaml.toYaml
+import java.nio.file.Path
+
+fun main() {
+    println(expectedWorkflow.toYaml())
+}
+
+val expectedWorkflow = workflow(
+    name = "Test matrix",
+    on = listOf(Push()),
+    sourceFile = Path.of("/tmp/some_workflow.main.kts"),
+) {
+    val strategyMatrix = object : StrategyMatrix() {
+        val os by iterate("ubuntu-latest", "windows-latest")
+        val node by iterate("14", "16")
+    }
+    job(
+        id = "test_job",
+        name = "Test Job",
+        strategyMatrix = strategyMatrix,
+        runsOn = RunnerType.Custom(strategyMatrix.os),
+    ) {
+        uses(SetupNodeV3(
+            nodeVersion = strategyMatrix.node
+        ))
+    }
+}
+
+val expectedMatrixYaml = """
+name: Test matrix
+on: push
+
+jobs:
+  build:
+    runs-on: ${expr("matrix.os")}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest]
+        node: [14, 16]
+    steps:
+      - uses: actions/setup-node@v3
+        with:
+          node-version: ${expr("matrix.node")}
+""".trimIndent()