Allow yaml-anchors in schema (#2200)

## Changes

Allows custom untyped fields in the root config in json-schema so it
doesn't highlight errors when using yaml-anchors.

Example use case:

```
tags: &job-tags
  environment: ${bundle.target}


resources:
  jobs:
    db1:
      tags:
        <<: *job-tags
    db1:
      tags:
        <<: *job-tags
```
  
One downside is that we don't highlight any unknown top-level properties
anymore (but they will still fail during CLI validation)

## Tests

Manually checked behavior in VSCode - it doesn't show validation error.
Also checked that other typed properties are still suggested

bundle/internal/schema/main.go

@@ -172,6 +172,15 @@ func generateSchema(workdir, outputFile string) {
 		a.addAnnotations,
 		addInterpolationPatterns,
 	})
+
+	// AdditionalProperties is set to an empty schema to allow non-typed keys used as yaml-anchors
+	// Example:
+	// some_anchor: &some_anchor
+	//   file_path: /some/path/
+	// workspace:
+	//   <<: *some_anchor
+	s.AdditionalProperties = jsonschema.Schema{}
+
 	if err != nil {
 		log.Fatal(err)
 	}

bundle/internal/schema/testdata/pass/yaml_anchors.yml

@@ -0,0 +1,11 @@
+tags: &job-tags
+  environment: "some_environment"
+
+resources:
+  jobs:
+    db1:
+      tags:
+        <<: *job-tags
+    db2:
+      tags:
+        <<: *job-tags