Ability to add custom fields for components

### Current Behavior

Right now we have identified components. These lead to opening of tickets in an issue tracking system. Currently there is no way to add custom fields to a component to extend functionality. Now we could track from our issue tracker for this one instance but other custom fields such as `owner` or `auditor` where you could select users would be great for tracking as an example.

### Proposed Behavior

It would be great if there was a way to have a `customFields` section that would allow users to add things like drop-down lists, user links, and text boxes to enhance tracking of issues found/raised in DT.

I could see the data structure from a response containing something like:

```json
"customFields": {
"owner": "dev1",
"auditor": "sysAudtor",
"IssueNumber": "12345",
"IssueUrl": "https://myjira.install/Proj1/12345"
},
```

### 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 enhancement was already requested

Start by reviewing how components are represented and returned by the API, then trace the existing component-to-issue-tracker flow. Define how a customFields response section would support text, dropdown, and user-link values, and confirm that those values can be stored and exposed consistently for components.

Written by the indexing model from the issue text.