Make artifacts.*.type optional in bundle JSON schema. (#2881)

## Why
It's not required for artifacts defined in DABs. We only support the
"whl" value for the type field in artifacts.

## Tests
Generated schema has type no longer required.

Author: shreyas-goenka

NEXT_CHANGELOG.md

@@ -17,5 +17,6 @@
 * Fix default-python template not to add environments when serverless=yes and include\_python=no ([#2866](https://github.com/databricks/cli/pull/2866))
 * Fix handling of Unicode characters in Python support ([#2873](https://github.com/databricks/cli/pull/2873))
 * Add support for secret scopes in DABs ([#2744](https://github.com/databricks/cli/pull/2744))
+* Make `artifacts.*.type` optional in bundle JSON schema ([#2881](https://github.com/databricks/cli/pull/2881))
 
 ### API Changes

bundle/config/artifact.go

@@ -22,7 +22,7 @@ type ArtifactFile struct {
 // Artifact defines a single local code artifact that can be
 // built/uploaded/referenced in the context of this bundle.
 type Artifact struct {
-	Type ArtifactType `json:"type"`
+	Type ArtifactType `json:"type,omitempty"`
 
 	// The local path to the directory with a root of artifact,
 	// for example, where setup.py is for Python projects