Add advertisments for third party dependencies before/after download

To get the best user experience from Cryptomator, users should install und setup third party applications.
If we display advertisement for those applications directly before/during/after the download of the setup program, we would have less user using old legacy components.

Start by reviewing the Cryptomator Website's setup-program download flow. The issue names no files or tests, so first clarify which third-party applications should be advertised and whether placement is before, during, or after download; done should be a defined, approved advertising experience.

索引モデルが issue の本文から書いたものです。