(dsl): Implement matchAll query

modules/library/src/main/scala/zio/elasticsearch/ElasticQuery.scala

@@ -45,6 +45,8 @@ object ElasticQuery {
 
   def exists(field: String): Exists = Exists(field)
 
+  def matchAll(): MatchAll = MatchAll()
+
   def range(field: String): Range[Unbounded.type, Unbounded.type] = Range.empty(field)
 
   private[elasticsearch] final case class BoolQuery(must: List[ElasticQuery], should: List[ElasticQuery])
@@ -72,6 +74,10 @@ object ElasticQuery {
     override def toJson: Json = Obj("match" -> Obj(field -> value.toJson))
   }
 
+  private[elasticsearch] final case class MatchAll() extends ElasticQuery {
+    override def toJson: Json = Obj("match_all" -> Obj())
+  }
+
   sealed trait LowerBound {
     def toJson: Option[(String, Json)]
   }

modules/library/src/test/scala/zio/elasticsearch/QueryDSLSpec.scala

@@ -94,6 +94,11 @@ object QueryDSLSpec extends ZIOSpecDefault {
 
           assert(query)(equalTo(Exists(field = "day_of_week")))
         },
+        test("successfully create MatchAll Query") {
+          val query = matchAll()
+
+          assert(query)(equalTo(MatchAll()))
+        },
         test("successfully create empty Range Query") {
           val query = range(field = "customer_age")
 
@@ -230,6 +235,19 @@ object QueryDSLSpec extends ZIOSpecDefault {
 
           assert(query.toJsonBody)(equalTo(expected.toJson))
         },
+        test("properly encode MatchAll Query") {
+          val query = matchAll()
+          val expected =
+            """
+              |{
+              |  "query": {
+              |    "match_all": {}
+              |  }
+              |}
+              |""".stripMargin
+
+          assert(query.toJsonBody)(equalTo(expected.toJson))
+        },
         test("properly encode Unbounded Range Query") {
           val query = range(field = "field")
           val expected =