DeathReaper: Move forum and currency choice handling outside

• This handling of the choice of forum was done internally to optimize the report generation which performs BMA and CS+ requests. In short, generating the report once for the two forums. But, with v2 switch by using the indexer it will become cheaper to make requests.
• The handling on which forum and for which currency should be done on an upper level, in a shell, CI config.
• It allows more flexibility, and makes the code less cumbersome.
• Make passing multiple forum (api keys) mutually exclusive
• CLI design choice:
  • --api-key and -du/-ml to select the forum
    • Disadvantages: One more option
    • Advantages: same option to set the api key
  • -du-api-key or -ml-api-key, which sets the api key and selects the forum
    • Passing one forum api key publishes on this forum, complex to understand

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• Disable publication on Duniter Forum