Get website certificate log with Filebeats

No, filebeat is only about collecting and shipping logs. It's not about executing arbitrary shell commands. One option would be (optionally with custom script) using a cron-job writing the log-file. Append date to log-file name to create unique filename per run + configure logrotate to delete old files + use filebeat to ship those logs.

Alternatively there is a community-beat (named execbeat) that might help here. But never tried it myself.