* [docs](function) add a series of date function documents
add docs for `hours_add`, `hours_sub`, `minutes_add`, `minutes_sub`,
`seconds_add`, `seconds_sub`, `years_sub`, `years_add`, `months_add`,
`months_sub`, `days_add`, `days_add`, `weeks_add`, `weeks_sub` functions.
When FE send cancel rpc to BE, it does not notify the wait_for_start() thread, so that the fragment will be blocked and occupy the execution thread.
Add a max wait time for wait_for_start() thread. So that it will not block forever.
This API can help user to get all create table statement of a given SQL.
So that it will be easier to run the case in other Doris cluster.
See document for details
