Add SUMM.AI budget for updating translations

[timobrembeck]

Motivation

We offer municipalities the option to purchase an extra 10.000 words for SUMM.AI update translations

Proposed Solution

• Create a new setting SUMM_AI_CREDITS_ADDON to define the amount for the SUMM.AI package, similar to DEEPL_CREDITS_ADDON
• Add new fields summ_ai_addon_booked, summ_ai_renewal_month and summ_ai_budget_used to the region model, similar to deepl_addon_booked, deepl_renewal_month and deepl_budget_used
• Whenever the content is translated via the new checkbox in the form, increase the used words budget of the region, see:
  • Add possibility to automatically update Easy German translations via SUMM.AI from page form #2110
• Show a graph of the used budget in the machine translation settings page

The initial translations via the bulk action or the management command should not drain the region's budget.

[osmers]

Just a small comment - I'm pretty sure we'd need this by July 1st as well since we offer the possibility of SUMM AI update translations from that point onwards.

[dkehne]

I will put that back into backlog because it is not as urgent as we thougt