move read transforms into "source" package as FeatureSources (#74)

* move read transforms into "source" package as FeatureSources

* fix core import spec validator to check for file.csv and file.json

* update import spec validator tests

core/src/main/java/feast/core/validators/SpecValidator.java

@@ -224,7 +224,8 @@ public void validateImportSpec(ImportSpec spec) throws IllegalArgumentException
         case "pubsub":
           checkPubSubImportSpecOption(spec);
           break;
-        case "file":
+        case "file.csv":
+        case "file.json":
           checkFileImportSpecOption(spec);
           checkArgument(
               !spec.getSchema().getEntityIdColumn().equals(""),
@@ -263,9 +264,6 @@ public void validateImportSpec(ImportSpec spec) throws IllegalArgumentException
 
   private void checkFileImportSpecOption(ImportSpec spec) throws IllegalArgumentException {
     try {
-      checkArgument(
-          Lists.newArrayList("json", "csv").contains(spec.getOptionsOrThrow("format")),
-          "File format must be of type 'json' or 'csv'");
       checkArgument(!spec.getOptionsOrDefault("path", "").equals(""), "File path cannot be empty");
     } catch (NullPointerException | IllegalArgumentException e) {
       throw new IllegalArgumentException(

core/src/test/java/feast/core/validators/SpecValidatorTest.java

@@ -670,10 +670,10 @@ public void fileImportSpecWithoutSupportedFileFormatShouldThrowIllegalArgumentEx
             featureGroupInfoRepository,
             featureInfoRepository);
     ImportSpec input =
-        ImportSpec.newBuilder().setType("file").putOptions("format", "notSupported").build();
+        ImportSpec.newBuilder().setType("file.wat?").build();
     exception.expect(IllegalArgumentException.class);
     exception.expectMessage(
-        "Validation for import spec failed: Invalid options: File format must be of type 'json' or 'csv'");
+        "Validation for import spec failed: Type file.wat? not supported");
     validator.validateImportSpec(input);
   }
 
@@ -685,7 +685,7 @@ public void fileImportSpecWithoutValidPathShouldThrowIllegalArgumentException()
             entityInfoRepository,
             featureGroupInfoRepository,
             featureInfoRepository);
-    ImportSpec input = ImportSpec.newBuilder().setType("file").putOptions("format", "csv").build();
+    ImportSpec input = ImportSpec.newBuilder().setType("file.csv").build();
     exception.expect(IllegalArgumentException.class);
     exception.expectMessage(
         "Validation for import spec failed: Invalid options: File path cannot be empty");
@@ -702,8 +702,7 @@ public void fileImportSpecWithoutEntityIdColumnInSchemaShouldThrowIllegalArgumen
             featureInfoRepository);
     ImportSpec input =
         ImportSpec.newBuilder()
-            .setType("file")
-            .putOptions("format", "csv")
+            .setType("file.csv")
             .putOptions("path", "gs://asdasd")
             .build();
     exception.expect(IllegalArgumentException.class);