debian/control: add Recommends on ca-certificates

waydroid init downloads from https URLs like
https://ota.waydro.id/system/lineage/waydroid_arm64/VANILLA.json which
will fail like this if the package ca-certificates is not installed:

ERROR: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (_ssl.c: 1029)>

Closes: https://github.com/waydroid/waydroid/issues/2034