[Bug] Goals: Fix schedules 'in between' calculation

[shall0pass]

The templates conditions were not finding a value when 'in between' was chosen from schedules. This adds a check on the schedule amount type, and if 'in between' is found will return the median value. I believe this matches the behavior of the scheduled transaction in the ledger. It may make more sense to fill the maximum amount here for a budgeted value. I'm interested in any comments on what the expected behavior should be.
 
Fixes: #1747

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packages/loot-core/src/server/budget/goaltemplates.ts	📈 +98 B (+0.30%)	32.13 kB → 32.23 kB

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[youngcw]

looks good to me