Policy condition PURL IS_NOT will match a substring

### Current Behavior

Define a policy with condition:
```
{
"subject": "PACKAGE_URL",
"operator": "IS_NOT",
"value": "pkg:maven/com.mysql/mysql-connector-j@8.0.33"
}
```
Upload a bom:
```
{
"bomFormat": "CycloneDX",
"specVersion": "1.5",
"version": 1,
"components": [
{
"type" : "library",
"group" : "com.mysql",
"name" : "mysql-connector-j",
"version" : "8.0.33",
"purl" : "pkg:maven/com.mysql/mysql-connector-j@8.0.33?type=jar"
}
]
}
```

Observe that the policy is not triggered.

### Expected Behavior

I don't think the behaviour is documented anywhere.
Yet I think it's reasonable to expect `IS`/`IS_NOT` operator requires equality, not being a substring.

### Dependency-Track Version

4.13.2

### Dependency-Track Distribution

Container Image

### Database Server

PostgreSQL

### Database Server Version

_No response_

### Browser

N/A

### Checklist

- [x] I have read and understand the [contributing guidelines](https://github.com/DependencyTrack/dependency-track/blob/master/CONTRIBUTING.md#filing-issues)
- [x] I have checked the [existing issues](https://github.com/DependencyTrack/dependency-track/issues) for whether this defect was already reported