e-mail attachment flow

[bikubi]

• implement similar to / within post-upload
  • different intro
  • with pdf redaction
  • different flow: keep request update parts (status etc.), remove/skip message parts (date etc.)
• update link in notification e-mails -- tested only up to a point, could not simulate this specific e-mail locally...
• renamed "post-upload" to "edit-message-flow", because it is used for non-postal e-mails now, too.
  • other ideas welcome.. i only had "message-upsert" as an alt :)
  • arguably edit-message-flow.vue (née post-upload.vue) could be split into sub-components, but with the flow graph, one-big-component-which-does-two-things might be the lesser evil
  • nb. https://github.com/okfde/fragdenstaat_de/tree/bikubi/email-att-flow matches the renames

[bikubi]

@krmax44 update summary:

• the "alpha" message block now shows all badges from the request page, including fails_authenticity and is_escalation
  • I had to fix one test, not sure, will leave a comment in code
• content_hidden, timestamps and layout are also closer now
• STEP_INTRO_EMAIL is its own SFC
• Problem? and Redact buttons work now
  • ~~hack~~ ~~trick~~ workaround to not rebuild them from scratch in Vue plus new API endpoints: I just used the regular forms
  • …with a special case to redirect to the email flow -- since we're only redirecting back to a landing page, this works out nicely
  • …but had to split them in two:
    • the trigger button is DjangoSlotted into the main Vue component
    • the modal part just renders into body- this seems to just work™
  • that content_hidden unhide button could work similarly
• There is still the prominent Answer button that now has no counterpart... :thinking:

⇒ if the form workaround is OK, feel free to review