Add VEX Support for ' Action Statement' in Dependcy Track

### Current Behavior

As per ["VEX" Min Spec](https://www.cisa.gov/sites/default/files/2023-04/minimum-requirements-for-vex-508c.pdf)

>
> For status "affected", a VEX statement MUST include one [action_statement] that SHOULD
> describe actions to remediate or mitigate [vul_id].

The logical map for Action Statement is [vulnerability->recommendation](https://cyclonedx.org/docs/1.5/json/#vulnerabilities_items_recommendation)

>
> Recommendations of how the vulnerability can be remediated or mitigated.

Within DependencyTrack, setting Analysis to "Exploitable" does not allow specifying a separate "Action Statement".
A logical fallback is "Details". However, details maps to [analysis->detail ](https://cyclonedx.org/docs/1.5/json/#vulnerabilities_items_analysis_detail) and not to vulnerability->recommendation.

### Proposed Behavior

For state 'exploitable', introducing/re-purposing a text box for providing `Action Statement` that maps to vulnerability->recommendation in the specification

### 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