mk-oracle: add simple Time‑Window Control for Custom Query Execution in Checkmk

Add the possibility to configure an execution interval together with simple time windows during which custom queries are allowed to run - for example, every 30 minutes between 08:00 and 17:00 from Monday to Friday, or once daily at 08:00.

When the current time falls outside the defined window, instead of executing the custom query, mk-oracle could return a standardized message such as:
“Skipping execution: outside check period.”

Benefits:
* Increased flexibility in query scheduling.
* More efficient use of resources by limiting checks to relevant time periods.
* Transparent and predictable query behaviour through clear feedback when executions are skipped intentionally.

Example Yaml configuration:
Schedule:
Mon:
- "0800-1100"
- "1300-1700"
Tue:
- "0900-1100"
Wed:
- "0900-1100"
- "1300-1700"
Sat:
- "0800-0805"