Docs: add a new cookbook for "how do I cron"

[jrkinley]

Issue description

Implementing a "cron" like pattern to control when a pipeline executes is a common request. Redpanda Connect can do this already, but the information buried in the documentation: inputs/generate.

Writing a specific cookbook for the cron pattern will provide users with more detail and make it easier to find and share.

Updates to existing documentation

https://docs.redpanda.com/redpanda-connect/cookbooks/

Link to Redpanda Slack conversation

https://redpandadata.slack.com/archives/C0731175XA4/p1737481988735849