Documentation for new webhook log clearing cron job

[RCheesley]

This PR seems to be missing the necessary documentation PR for the new cron job / explanation of the feature. Adding to the education team's backlog!

Originally posted by @RCheesley in mautic/mautic#10405 (comment)

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[vickywane]

Hi @RCheesley ,

A PR documenting the CRON job is something I'd like to work on.
Has any internal update been made on it since your last update?

If not, I'd like to take this up.

[RCheesley]

@vickywane great - the PR with the information about the new cron job is at mautic/mautic#10405 (comment).

We should probably work on the new docs repo at https://github.com/mautic/user-documentation though, I think!

Will align regarding this on Slack.

[vickywane]

Nice.

I'll reach out on Slack.

[favour-chibueze]

@RCheesley @vickywane I have submitted a PR on cron jobs. Currently working on the setup section. You can work on any other section @vickywane