Migration should notify of skipped resources

### What problem are you facing?

When creating a migration on a local filesystem if a file contains unknown Kinds, the migrator will not process the file without emitting any warnings or errors.

For example, if a manifest contains a `Secret` which does not have a registered converter, outputs are never generated.

```yaml
---
apiVersion: v1
kind: Secret
metadata:
name: demo-foo-mq-rabbitmq-creds
namespace: example
annotations:
argocd.argoproj.io/sync-wave: "-2"
type: Opaque
immutable: true
data:
password: "cGFzc3dvcmQK"
---
apiVersion: mq.aws.crossplane.io/v1alpha1
kind: Broker
metadata:
labels:
crossplane.io/provider-version: v0.26.1
name: demo-foo-mq-rabbitmq
namespace: example
annotations:
argocd.argoproj.io/sync-wave: "1"
spec:
forProvider:
region: us-east-1
engineType: RabbitMQ
publiclyAccessible: false
autoMinorVersionUpgrade: false
engineVersion: 3.8.11
hostInstanceType: mq.t3.micro
deploymentMode: SINGLE_INSTANCE
subnetIDs:
- subnet-2cc5ce61
securityGroupIdRefs:
- name: demo-foo-mq-rabbitmq-security-group
users:
- username: rabbitmq-admin
consoleAccess: true
passwordSecretRef:
key: password
name: demo-foo-mq-rabbitmq-creds
namespace: example
tags:
App: crossplane
Environment: qa
Name: crossplane-mq
Product: crossplane
Squad: sandbox
Tier: backend
VS: sandbox
cluster: mq-cluster
writeConnectionSecretToRef:
name: demo-foo-mq-creds
namespace: example
providerConfigRef:
name: awsconfig

```

The generated migration plan is mostly empty and none of the other directories are crated.

```yaml
spec: {}
version: 0.1.0
```

### How could Upjet help solve your problem?

The user should be informed of any local filesystem resources that have been skipped during processing.