handling rate limits to get past the 100 domains per csr letsencrypt limit

[matiu2]

Letsencrypt rate limits allow up to 50 CSRs a week and 100 domains per CSR. (Note that a www.mydomain.com + mydomain.com counts as two certs.)

If plesk has more than 100 domains with letsencrypt, it should break them down into multiple CSRs. Currently it tries to put them all on one cert, and hits the 100 limit, and lets encrypt rejects it.

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As a side note, perhaps we could store the lets encrypt rate limits in the extension options, so that if they change, we can notify the extension of the new settings manually.