docs(connectors): Push to Connector shows only when a connector covers the finding

[blakeaowens]

Description

Docs for a set of Downstream Connector fixes in DefectDojo Pro (paired with a Pro PR):

• Downstream Connectors (connectors/downstream/about.md):
  • The gear menu offers Push to Connector only when an Issue Tracker Assignment covers the Finding or Finding Group; the edit form and Bulk Edit still offer it and explain an uncovered push.
  • A grouped Finding is reported as sent as part of its Finding Group, and a push that reaches only some connectors says how many it missed.
  • While a push runs, the gear shows a spinner and cannot start a second push.
  • The Assignment form's pickers list only Assets and Engagements the user can edit, and Edit and Delete appear only on editable Assignments.
  • Deleting a Mapping or connector is refused when it would remove Assignments the user cannot edit.
  • Errors and ticket links follow the user's access to the Finding, and the pages require Integration View.
• Jira (connectors/toolreference/jira.md): what DefectDojo reports when Connect With Jira does not complete, and that the permission is checked again on return.

English pages only; the language copies are generated from them.