kafka-source defaults saslAuthType to NONE without the not-secured naming its siblings use

`kafka-source` declares:

```yaml
saslAuthType:
title: Authentication Type
description: Authentication type to use. Use NONE for no authentication, PLAIN or SCRAM_SHA_256/SCRAM_SHA_512 for username/password, ...
type: string
default: NONE
enum: ["NONE", "PLAIN", "SCRAM_SHA_256", "SCRAM_SHA_512", "SSL", "OAUTH", "AWS_MSK_IAM", "KERBEROS"]
```

With `NONE` and no SSL, the connection is plaintext and unauthenticated out of the box.

The catalog already has a convention for Kamelets that ship in that posture — six `kafka-not-secured-*` Kamelets state it in the name. `kafka-source` does not, so the name suggests a secured default that the schema does not provide.

Options, roughly in order of disruption:

1. Make the security selector required (no default), forcing an explicit choice.
2. Change the default to a secured value.
3. Split into `kafka-source` (secured default) and a `kafka-not-secured-source` sibling, matching the existing convention.

Option 1 is probably the least disruptive while still removing the silent-plaintext default, but this is a catalog-convention decision rather than a mechanical fix — flagging for maintainer input before anyone implements it.

_Claude Code on behalf of Andrea Cosentino_