[6.x] Add config to disable HandleEntrySchedule job

[duncanmcclean]

This pull request adds a handle_scheduled_entries config option, which allows the HandleEntrySchedule scheduled task to be disabled.

Statamic registers this scheduled job unconditionally, and runs it every minute:

$this->app->make(Schedule::class)->job(HandleEntrySchedule::class)->everyMinute();

It's fine on traditional hosting, but becomes a problem on usage-billed platforms (like Laravel Cloud or Vapor) as it means the application's resources need to boot every 60 seconds to run the job, whether or not the site has a single scheduled entry.

This PR adds a config option so those sites can opt out:

'handle_scheduled_entries' => env('STATAMIC_HANDLE_SCHEDULED_ENTRIES', true),

Disabling the job won't prevent entries from being published on time. Entry::status() derives scheduled from the entry's date on every read, so an entry goes live either way. The job only dispatches EntryScheduleReached, which invalidates the static cache and updates search indexes — so what you lose is those two staying in sync until something else touches the entry.

The original request asked for a configurable frequency rather than an on/off switch. I've gone with a boolean because the two aren't equivalent — MinuteEntries looks at exactly one minute, so running the task every fifteen minutes would skip fourteen of them rather than publishing late. Supporting a frequency means reworking the job to sweep the whole elapsed interval and persist its last run, which felt like more than this needed. A boolean can widen to accept a frequency later without a breaking change.

Closes statamic/ideas#1476

[4rn0]

Lovely gents!