docs: table column customization in the Pro UI

[blakeaowens]

Description

Adds a documentation page, docs/content/navigation/PRO__table_customization.md, describing how to customize data tables in the DefectDojo Pro UI: choosing which columns are visible, reordering columns, resizing columns, and saving those settings as named table preferences.

This documents a new Pro capability (drag-to-resize column widths that save to table preferences) shipping on the same release line, and consolidates the existing column-picker, reorder, and saved-preference behavior in one place under "Navigating DefectDojo".

Points covered on the page:

• Choosing visible columns via the column picker.
• Reordering columns by dragging headers.
• Resizing columns by dragging a column's right edge, including that each column has a minimum width and that the selection and row-menu columns are fixed.
• Saving table preferences (Save as New Preference, Save Column Layout, Save Filters and Sort, set default, duplicate, rename, delete, reset) and how shared preferences behave.

Test results

Documentation-only change: one new Markdown page, no code paths affected, so there is nothing to unit test. Rendered locally to confirm the formatting and front matter (title, description, weight) match the sibling pages under navigation/.

Documentation

This PR is the documentation change.

Checklist

• Rebased against the latest bugfix.
• Submitted against bugfix (docs ship alongside a Pro change on the same release line).
• Meaningful PR name.
• Documentation added under docs/.
• Not applicable: no code, no migrations, no unit tests, no settings changes.

Suggested label: documentation (or maintenance).